I think the best thing is to balance these out a little bit. Go with the strengths, but have a few feats/powers to shore up the weaknesses some.
Really I don't think the characters even matter, it's the synergy that matters. For instance, at level 1 if 4 characters use -2 AC until next round powers and can keep an opponent's AC effectively reduced by 8 for the encounter, how much worse is it than -8 at level 24 with higher level powers? That to me seems to be whats really being tested. The roll against AC is supposed to be fairly constant, so if that number changes from 8 then there is a change in the synergy's power.