Only FFVIII gives FFXII a running in the "I can kill bosses with like 2 uber attacks" category. All the rest (Gil Toss, Aeon Spamming, Dark Knight Dressphere etc) just make battles that would have otherwise been rather challenging fairly easy.

And I can't think of anything in FFIII that can be abused. There is the Ninja/Sage jobs from the original, but that wasn't so much "they make the game easy" as it was "they make the make the final boss less insane".