Quote Originally Posted by T51R View Post
I think this was explained by Ken actually being a genius when it comes to Ansatsuken, but since he never gave himself to it like Ryu did he never even began to explore his potential(and thus also avoided the Satsui no Hado) Also explains why Akuma just doesn't care about him.
As far as I recall, this is the official reason (I don't know a lot of SF lore, but I remember reading this). As it turns out, Ken is actually a better natural fighter than Ryu, and kind of coasts on that. The reason Ryu is equal to/better than him is because Ryu trains absolutely obsessively.