It used to be a big frustration in Dragonspyre that almost every battle you fought the creatures use weakness spells against you. I heard before the Celestia update that this was going to be fixed so less creatures that were not Balance school would not use weakness spell so much. I haven't actually played much in DS lately so I am not sure how that has panned out. However I have been playing in Mooshu (cave of Solitude) and Grizzleheim (Savarstaad Pass) and was getting frustrated that half the battles I fought the creatures use weakness spells. It really gets annoying when so many non-Balance creatures use it. It would be nice if you had different strategies for the different schools when you fight them, but when they all use weakness it gets so repetitive. I don't mind at all when Balance creatures use it, and I have come to expect to deal with it in boss battles but why do so many non-balance creatures have that spell? If you want to make the creature battles tougher than just give them more health or have them use shields.
Weakness was definitely over-used in the game and is particularly prevalent in Dragonspyre. Don’t expect to see it used nearly as much in Celestia as we don’t like the degree to which it slows down combat.
I agree that weakness is being used by the enemy way too much. In the last couple of days, I have been running my life wizard in Mooshu and Dragonspyre working on some badges. In Dragonspyre, I was hit 4 times in one battle with weakness and 3 times in Mooshu in one battle. I expect to get hit with it occasionally, but that was just TOO much.