I'm okay conceding that Bob Hayes is the fast man in NFL history.
However, as with any argument, time and era make the debate sort of irrelevant.
For example, Bob Hayes TRAINED as a world class sprinter. You don't get to the Olympics merely stepping onto the track. You practice hand position, knee lift and work extremely hard to run at your peak level.
Deion played football, baseball and basketball. (Same thing with my oldest son. Was extreme fast when he was younger but didn't run track. Instead, played football, baseball, basketball and wrestled before getting into track in high school. I told him had he run track at the beginning, he would have been world-class by his high school year, even though he's still fast.) To my knowledge, Deion never ran track. Or if he did, he didn't spend a long time in it. (Wikipedia page doesn't acknowledge he ran track.)
In fact, there are varying reports of how dedicated Deion was to training. Some say he really didn't train that hard. Others, like Michael Irvin, say he was a very hard worker.
I said all this to say, image if Deion Sanders trained for track like Bob Hayes did. If he did, I doubt very seriously Hayes would beat Deion. Hayes was 5'11. Deion 6'1. Deion had longer legs. And if he took part in the stretching exercises that sprinters CONSISTENTLY do, he would have been even faster because he would benefit from looser hamstrings. Any time you can not train, not stretch, run a 40 and run it 4.2? Uh, you da FAST!