Heroes 6 - Discussion

What's wrong with powerful abilities? The main thing is that they should be:
a) Interesting
b) More or less balanced
c) There shouldn't be a situation where one ability affects a huge number of parameters, like with the knight's debuff that you mentioned as an example. One or two truly significant changes to something. It's better to avoid changing parameters (if not everywhere, then at least more often), and instead use bonuses of a different type that cannot be set through parameters (like the rain of arrows or elemental vision in the fifth part).