Development cannot be looked at on a one-off basis, imo. If you take 5 kids at DB and 1 improves a lot and 4 don’t, did you ‘develop’ him? What about the other 4? How do evaluations fit in? Maybe the kid was well chosen and he ‘developed’ himself - the way kids do at plenty of other schools around the country. (Worked hard, took advantage of S&C, etc.).
For ‘development’ to have meaning separable from evaluations, you need a way to measure value-add once a kid gets to campus, as opposed to before a kid gets there (which is what evals are about). It’s very hard to separate those two traits and yet they are really different.
Also, probably the most important aspects of development are about how a kid performs IN COLLEGE. Looking at the nfl draft for evidence is flawed, imo, for two reasons - because it is a small and skewed subset of the kids you’re trying to assess, biased towards athletic ceilings rather than actual development or college contributions, and because the goal of a staff is to win games not create draft picks. It’s complex to assess these things, though, because performance in college is a function of the guys around you, scheme and game planning, not just development. It’s harder to shine when you’re not put in a position to shine by a coach, or don’t have someone to get you the ball, or block.
I have long said on this site, people use development as a label without understanding it (@franchise saying similar point I believe). I don’t know how to prove it/measure it, but I would suggest it comes in 3 parts: helping kids harness their athletic talent, helping kids build their physical capabilities, and helping kids refine their technique. S&C is measurable. The other two, not so much.