Actually, Pichu is a lot worse than Mewtwo as Pichu is placed as the worst character in Melee. Which means Pichu is the weakest Pokemon in its games. This caused me to hate Pichu in general and wishes everyone to do the same.
Smash Bros. has NOTHING to do with ANYTHING.
Yes it does, the Pokemon in the Smash Bros. series are staying true to their in-game incarnations alongside with every other Nintendo character who are playable there.