What does 過去へ遡るほど大きいとされる refers to here?

Question

華族制度が今なお存在する（成立時期も約300年前と古い）世界。歴史上江戸時代および鎖国が存在せず、西洋文明の普及が早いなどもうひとつの世界との差異は過去へ遡るほど大きいとされる。

This is an entry about a fictional parallel world of the novel 'ぼくのご主人様 ' i understand this as ; from a historical perspective the edo period nor the sankaku period existed and the differences of ( the original world ) with the other world is made big as if you went back in time . deepl however translate this is as : 'differences between the (parallel word ) and the of the world ( the normal one ) are said to be greater the further back in history one goes, such as the absence of the Edo period and national seclusion, and the rapid spread of Western civilization' .

So, does 遡るほど大きいとされる mean the further you go back.... ? https://ja.wikipedia.org/wiki/%E3%81%BC%E3%81%8F%E3%81%AE%E3%81%94%E4%B8%BB%E4%BA%BA%E6%A7%98!%3F

Answer 1

• 差異は過去へ遡るほど大きい is the same as 差異は過去へ遡れば遡るほど大きい. It's a shorter version of the ～ば～ほど construction. See: Can 「XければXほどY」 clause pattern be shortened to 「XほどY」?
• とされる is the passive version of とする ("to claim", "to consider"), so it's "it is considered that ～" here. See: What does this としています express?, What is the difference between として and とする? and What does として mean here?

歴史上江戸時代および鎖国が存在せず、西洋文明の普及が早いなどもうひとつの世界との差異は過去へ(遡れば)遡るほど大きいとされる。

As can be seen from the absence of the Edo period and national seclusion, and the earlier spread of Western civilization, it is considered that the further back in time one goes, the greater the difference from the other world becomes.