Pretty sure he's said as much.
Have seen very little of Cooks, but what set Smitty apart from other small receivers was his strength and leaping ability. He had great leaping ability and great timing and that combined with his physical strength allowed him to play much bigger than his size.
I'm using the past tense here because Smitty is no longer that guy. Age has finally caught up to him. He's still a damn good receiver, but he's no longer what he once was which is true of damn near everyone who is in their mid-30s.
Smitty has more physical advantages than those you named. He tracks better than almost anyone in the league, he has amazing balance, and he also has amazing agility. He is a genetic freak, a gymnast who can run at light speed and is tough as nails. Typically guys built like that arent elite fast, theyre just quick in acceleration and changing directions, Smitty was all of the above. There will never be another. . . and ya sucks that his best days are behind him, but plenty of good ones are still out there to be had.