Coleman is not slow, he just ran a slow 40yd dash, there's a difference. The 40 is a track event- not a football event. His track start was awful & clearly cost him time. It's a good thing that 0% of routes in football require you to start in a track stance. I'd bet if Coleman spent a week or 2 with a track coach he'd run 4.50ish, without even getting any faster, just learning how to start properly.
The 40 is a great indicator of overall speed, but only if you master how to run it. It can be a poor indicator if track form is out of whack.
Exhibit A: Go watch Josh Allen's 40 from the combine, it was horrendous. It looks like he never trained with a track coach before the combine, his start & running technique are so wrong. Josh is so much faster in game than he showed in this track drill while wearing shorts.
We should be thankful that he ran a 4.6, because if he ran a 4.50, he wouldn't have made it to us in the draft.