CaptRory kind of hit on a version of the point I was going for. Part of it depends how D&D-ish you want your game to be. BESM (or M&M or Wild Talents, etc., they all share the same DNA, which I suppose is Champions and the precursor to that whose name escapes me) are really open-ended in a lot of ways. But, that means they kind of chucked game balance out the window, to greater and lesser degrees.
D&D is characterized with more of a ... I don't know, menu approach. I'm sure there's a more sophisticated term for it. You are picking combinations of abilities. And, to keep that interesting, there are a great many abilities to combine and they should, ideally, do a great many things. Otherwise it's just monotony and you just pick the best one, viz. the orgy of guns in Rifts.
Once you're in that universe, though, the probability of something being imbalanced is very high. Which, credit where it is due, is exactly what CaptRory says above. On the other hand, looking for kickass combos is, to some extent, the game. At least mechanically-speaking.