Sorry, my reply post got killed by a reboot. @
Angrymesscan, that's essentially it.
Each risk factor makes success harder, and the initial hill is steeper for rookies. Drugs increase the risk.
I also believe DE's who have to face down bigger and longer-armed OT's are going to get beat up, and so they need more muscle and power (hence, size) to withstand this and more importantly dish out more punishment.
Gregory, IMO, was set up to fail the moment we threw him to the wolves day one instead of making his PT in crease gradually.
Anyways, this website does some interesting studies, and in particular this combine analysis from a couple years back:
http://harvardsportsanalysis.org/2015/02/the-combine-actually-matters-part-2/
It showed some raw combine stats when matched against successful players (based on in their first 3 NFL seasons) correlated more strongly to success than others, and differently for different positions.
These are raw, unbiased numbers and reflected in the chart below.
Colors increasing in brightness from black to brightest green show the degree of correlation from a stat to successful first 3 seasons for each position.
Weight, more than any other stat for any other position correlated most strongly to success for DE's. At the other end of the spectrum the study found that WR success had no correlation to any stat at all.
This does not mean a 400 pound jackass is going to be a HOFer. You still have to make it through the selection process and actually be skilled-- so as
Angrymesscan pointed out most other factors are canceled out.
Lot of interesting stats, like how 40 times correlate strongly to ILB success but barely a blip for FS's or WR's.