Well, I think the real issue is people making a big deal about a tenth of a second difference between some of these guys. A 4.5 is not much different than a 4.4.
And you are never just running in a straight line on a football field anyway. You are fighting off press coverage, running routes, reading the zones, hand fighting with defenders, etc.
So, yeah, a 4.3 is faster than a 4.4, a little, but it is not significantly faster in field results and there are countless other factors to consider with deep ball success. I think the #1 and #2 attributes are route running and ball tracking. I played some receiver growing up and tracking the deep ball was very difficult for me. It's a real skill.