It is though. Wrs and players almost never stick around long after losing a step and seldom are more than a fraction of their former level of play.
You can't defend some one running away from you. Guys like oj Simpson blink and countless others have made hof careers out running perfect pursuit angles.
Countless guys with great speed have become functional route runners and catchers more players have been developed at all levels because they have speed with out any football tools than any other kind of split.
I'm sure the league will step in at some point.