IMO, people who play 3D fighters don't need their own control scheme in a 2(.5)D fighter...
I don't think it was the two attack buttons that made it seem like the "easy mode", it was the trade for motions like (presumably) 236X for being a followup to a normal (P->P is a bit easier to mash out... although you have that balance issue you mentioned in the OP since it's followup only...)
If you can find a way to do it well, that'd be great, but imo it's not a good idea...