Difficulties in the question
There are a couple of points in the question where I suspect that it is misinterpreting the Wikipedia article on the Alexander Romance.
The question says, “Looking into the matter, it seems the Greek version is voluminous” but the link is to a list of Greek versions of the romance, with no mention of the length of any of the versions. Perhaps the word “recensio” (Latin for “recension”) is causing difficulty? In context this means, “a family of manuscripts of a work sharing many similarities, possibly deriving from a common source”. For example, “recensio β” is a version of the romance appearing in nine manuscripts from the 11th to 16th centuries.
As for the length of the romance, the critical edition of recension β has 207 pages of Greek text, but about half of that is the critical apparatus. So the 188 pages (not including introduction and notes) of the 1991 Penguin edition are not unexpectedly short, and I don’t see any evidence that this has been abridged.
The question says, “most of these recensions and translations are from the Victorian era” but this is not the case. It’s important to distinguish between the different dates associated with a work. For example, in the case of recension β, there is a 1965 critical edition edited by Leif Bergson, which appears in the list in Wikipedia. This is based on a family of nine manuscripts, the earliest of which is Codex Parisinus Supplementarius 690, dated to the 11th century. But the work itself must be much older than that, the original manuscript being now lost.
English versions of the romance
These derive from various sources—the Stoneman, Dowden, and Haight translations are from Greek; the Wolohojian translation from Armenian, the Kazis translation from Hebrew, the Budge translation from Syriac, and the medieval versions from French or Latin. I’ve sorted these into reverse chronological order, as I guess that you might not be so interested in the medieval versions.
I think the best way to compare these different versions of the romance is to see how they treat a single episode. I’ve picked the murder of Alexander’s father Philip II of Macedon by his bodyguard Pausanias of Orestis.
There was a certain man named Pausanias, a rich and powerful man and ruler of all the Thessalonians. This man conceived a desire for Olympias, the mother of Alexander, and sent some powerful men to persuade her to leave Philip and to marry himself, he also sent a good deal of money. When Olympias would not agree, Pausanias came to where Philip was, in the middle of a theatrical performance. He knew that Alexander was away on campaign. Philip was taking part in the contests in the Olympic theatre when Pausanias came in, armed and accompanied by several of his nobles, with the intention of murdering Philip and seizing Olympias. He stepped straight up to him and struck him in the chest with his sword, but did not kill him. There was a tremendous uproar in the theatre. Then Pausanias rushed off to the palace to seize Olympias.
Richard Stoneman (1991). The Greek Alexander Romance, p. 55. Penguin.
There was a man called Pausanias in Pella, a man of importance and great wealth who was the leader of all the Thessalonicans. Now, this man had fallen in love with Olympias, Alexander’s mother, and sent some people to her to persuade her to leave Philip, her husband, and marry him, sending her many gifts. But Olympias refused; so Pausanias headed for the place where Philip was, having discovered that Alexander was away at war, and arrived as a stage competition was being held.
Philip was conducting proceedings in the Olympic theater when Pausan-jas appeared, sword in hand, in the theater with a number of other brave men, with the intention of killing Philip so that he could seize Olympias. He attacked him and struck him in the side with his sword but failed to kill him. Pandemonium resulted in the theater. And Pausanias rushed off to the palace to seize Olympias.
Ken Dowden (1989). The Alexander Romance, pp. 669–670. In B.P. Reardon, ed. (1989). Collected Ancient Greek Novels. Berkeley: University of California Press.
And there was a Thessalonian nobleman by the name of Pausianos, who had a large personal army and huge wealth. This man lusted for Olympias, and secretly sent men who could gain her trust so that he might persuade Olympias to leave Philip and become his wife. But Olympias did not agree to do this. And Pausianos made the following plan upon learning that Alexander was going to war and that there was a concert of performers of all kinds of artistic songs taking place and that Philip was at the concert. Pausianos, bared sword in hand, entered the theater with other brave men, intent on killing Philip so that he might abduct Olympias. And with his sword he struck at Philip’s side, and he struck him hard, but he did not die. There was a huge crowd in the theater, and Pausianos rushed to the palace with the intention of abducting Olympias.
Albert M. Wolohojian (1969). The Romance of Alexander the Great, pp. 44–45. New York: Columbia University Press.
In those days there was a king in the land of Bithynia whose name was Pausanias. Although this king was mighty and strong, he paid tribute to King Philip year after year. For a long time Pausanias had coveted Queen Olympias, the mother of Alexander. Pausanias rebelled against King Philip, gathered many horsemen and a large army and invaded Macedonia. When King Philip heard that Pausanias had transgressed and rebelled against him and had invaded his country, he was filled with anguish and his heart was sorely grieved. He went forth to meet him with a small number of men because he had sent his army with Alexander to fight against his enemies. Pausanias’ men fought against Philip’s men and defeated them. Philip turned his back in flight, but Pausanias pursued him, struck him and stretched him out on the ground. He did not die immediately. However, he was benumbed and was like a corpse lying in the field.
Israel J. Kazis (1962). The Book of the Gests of Alexander of Macedon, p. 71. Cambridge, Mass: Medieval Academy of America.
There was a man called Pausanias, an important person, a wealthy Thessalonian, and he had a very large and powerful army. He fell in love with Olympias and sent minions to persuade her that she should leave Philip and marry him. Olympias did not agree to this. So Pausanias conceived a scheme, and made inquiries about Alexander to find when he would be out of the country. And when the time came and Alexander was at war with certain cities and the dramatic contests were going on, Pausanias learned that Alexander was abroad and Philip was at the festival. So he went, sword in hand, and hurled his weapon at Philip and was successful in stabbing him through the ribs. He did not die at once. There was great excitement in the city. Pausanias made haste to enter the palace while Philip was still alive, wishing to carry off Olympias.
Elizabeth H. Haight (1955). The Life of Alexander of Macedon. New York: Longmans.
And when Alexander had departed from his father, a certain man named Theosidos—a small man and slight in body, purseproud and honoured because of his money, who had come from the land of the Thessalonians and had a multitude of slaves, and whose mind and heart were inflamed with love for Olympias, and because of his love for her he gave goods and gifts to many people of the city, and communicated his secret to them—this man sought to slay Philip by some means, for he saw that Alexander was not in the country. Now in those days there was in the city an amphitheatre which was called the Olympic, and certain people, partisans of Theosidos, by his instruction and advice, begged Philip with tumult and clamour to go with them and see the contest of the athletes. And Philip, because he was unacquainted with the craft of Theosidos, was persuaded to look on with them. Now in the middle of the spectacle the partisans of Theosidos made a disturbance and an uproar in the theatre by his advice and command. Theosidos himself was outside the theatre, and when he heard the uproar and disturbance, he rejoiced, and together with his partisans armed himself and went into the theatre, and gave people to understand that he had come in to assist Philip. Then he brandished the spear that was in his hand, and pretending that he was going to smite another, cast it and pierced the heart of Philip, whilst feigning to be a helper of the king. Philip straightway fell to the ground, and Theosidos with his companions went out at once from the theatre, because they thought that Philip was already dead, but his life yet remained in him.
Ernest A. Wallis Budge (1889). The History of Alexander the Great, pp. 31–32. Cambridge University Press.
Ane gret lord quhilk held land of Philipone,
His leige man, was callit Pensomas,
Quhilk of ane cuntre callit Brytagne was,
Sone and are to ane callit Corestes,
The quhilk was cousing to erle Arestes,
Quhilk of befoir rych enamorat haid bene
Off his mother, Olimpeas be quene,
For guhan he saw bat Alexander was past,
And neuer to cum agane pair, as he traist,
He semblit of his freindis ane gret menze,
And furth-with in Macedone past he,
And thocht a sege to be palace lay.
[… lines 2362–2384 omitted …]
Bot or he [Alexander] com, þe battall end haid tane,
And Pensomas to be palace gane,
And Philip left woundit in be feild,
In point of ded lyand vnder scheild,
And all his men war tane, or slane, or fled.
Gilbert Hay (1499); John Cartwright, ed. (1986). The Buik of King Alexander the Conquerour, lines 2350–2391. Scottish Text Society.
An in þe mene tyme, whils he was þare, a lorde of Macedoyne þe whilke highte Pansamy, a strange man & a balde, suget vn-to Philippe, and hade of lange tyme couette for to hafe þe quene Olympias, conspirede agaynes þe kynge, and come with a grete multytude of folke appon þe kynge, to for-do hym. And when tythyngeʒ here of come to kyng Philippe, he went to mete hym in þe felde wit a fewe menʒee. And when he sawe þe grete multitude þat Pansamy hade wit hym, he turned & fledd, and Pansamy persued after hym, and ouerhied hym, and strake hym thurghe wit a spere, and ʒitt ife all he were greuosely wonded, he dyed noʒte alsone, bot he laye halfe dede in the waye.
Anon (c. 1440); J. S. Westlake, ed. (1913). Prose Life of Alexander, p. 12. Early English Text Society.
Then was a man in massidon · þat in þe marche dwellyd,
A proved prince & a proude · pausana he heght,
A Bigg berne & a bald · in brenes to ryde,
Þe sonne of one sorastes · als says me þe text.
This freke of all þe fraunches · of kyng philop haldes,
And was sogett to hym-seluen · & seruage hym awght.
Bot ʒett depely mony day · desirred he þe whene,
And leued vnlappyd with hir loue · mony lang wynter.
And be þat cause to þe kyng · he kest suche a hate,
þat he desired hys deyde · & dight hym þarfore.
All þe folke of hys affinite · he fresly assemblez,
And sekez owt with a hoge some · a-sawte hym to yelde.
When philip herd of þis fare · grett ferly he thynkez,
Ferkez forth with a few folke · & hym in feld metes,
Seys þe multitude so much · of men þat he brynges,
Brades toward þe burgh on hys blonk · & hys bak shewys.
Þan scrikes shilly all þe shalkys · & shotes at onys,
And pausana þe prince · vpon a prouude stede
Sprynges forth with a spere · & spedes hym after,
And þorow þe bake in-to þe brest · hym berez to þe erth.
Anon (c. 1400); Walter W. Skeat, ed. (1886). The Wars of Alexander, lines 913–932. English Early Text Society.
A riche baroun in Grece was,
His name was hote Pausanias,
That loved muche Olimpias.
So he yede, and so he sent,
By writes, and by riche presentis,
That he dude, in bedde stille,
By the lady al his wille.
And bytweone heom heo hadde y-spok,
Of kyng Felip to beon awroke.
Womanis herte is unwreste!
Heo wol beo wroke, othir to-berste!
By heore bothe compissement,
Kyng Felip was wounded, verament,
Dedly woundid thorugh the nape,
That he no myghte deth ascape.
Anon (c. 1300); Henry Weber, ed. (1810) Kyng Alisaunder, lines 1334–1348. In Metrical Romances of the Thirteenth, Fourteenth, and Fifteenth Centuries, volume 1, p. 60. Edinburgh: Archibald Constanble.
