I wasn't even watching the anime when R/S/E came out, Blaziken's moveset was just too competent compared to a lot of other types/type combinations. As far as Pokedex info, Blaziken is a very powerful running and kicking Pokemon. As a fighting Pokemon Blaziken would be a great antithesis of Mewtwo.
But the anime did contribute quite a lot, especially where Pokemon voices are concerned. I would have preferred Ash and his 3 Kanto starters rather than a generic Pokemon Trainer though.
I loved Mewtwo's animations in Melee. And while he was an antagonist of sorts in the anime, the Stadium games really cemented his position as an 'ultimate Pokemon'.
and what's this about Ryu? If Capcom's top fighter can't appear in a fighting game then the world might as well end.
Besides I think Hadoukens would be a lot more annoying in another fighter: the Tekken crossover.