The biggest problem with Fox/Falco similarity isn't how they play, but how they appear to play to the average player.
Your ordinary kid playing Brawl would see Fox, Falco and Wolf as slight variations of the same character. Press B, and they shoot their gun. Up+B, and they stand still for a bit before rocketing up. Side+B, they flash sidewards. Down+B, they activate their shields. Their final smashes are the same. Yeah, some of them will feel more sluggish than the others, some will fall faster and some have different hitboxes, power or animation for the same moves, but ultimately they appear to do exactly the same as one another. "Professional" players know that this is not the case, but to those not bothering to go as deeply into the game, the three are quickly scoffed off as "lame clones". I really hope they will try to differentiate them more in the next game.