In fact this is a case of a pretty simple and straightforward verse that has been unnecessarily complicated by its translators. The word in question ירב pretty much translates into fight, contend. See Hosea 4:4, and Strong's concordance. In fact almost all modern translations agree that this is the basic meaning of this word albiet with minor modifications. In this case we may say that the Tyndale commentary is coming from left field!
The Tyndale commentary was apparently unhappy with the conventional trnaslation (the reasons for this is unclear) so he sought ways to alter the meaning of this word. He imagined ירב as a shortening of the common Hebrew word ירבה which means increase, thereby he constructed this odd and awkward phrase, "Let Baal give increase". What the intended meaning is supposed to be, according to this interpretation, is entirely unclear to me. If it is meant as a blessing to Gideon, as the OP understands, then I am left wondering why Baal would give Gideon, his archenemy, his blessing (he just smashed his altar)?
Secondly, if Tyndale wanted to be loyal to the text he should have translated thus: "Let Baal increase in him". Instead he modified it to his liking and got his desired "Let Baal give increase", and ignored the rest! I should also add that it is rare in biblical Hebrew to use the word ירבה in conjunction with a person, it is usually used in conjunction with money, silver and gold, children, etc. but to say it on a person, "let Baal increase him", I think is at best outlandish! Why not tell us what Baal would increase: Money or children? Why leave us hanging in the middle?
So I reiterate, the conventional translation in this case is actually the correct translation of ירב. There is no point in asking why they put a curse on Gideon after he smashed their beloved god Baal, something which is to be expected. There is no need to resort to unorthodox approaches when the meaning is as clear as day.