It’s everything. I can’t speak to every other team in the NFL, but the Patriots system for evaluating draft prospects is about specifically telling how the player would fit into the current team, how they compare to the players already on the roster, and whether they’d be a starter, backup or roster bubble type.
It’s hard for everyone, including the NFL teams themselves, to truly know how an athlete will develop as a professional. I think that’s true of any profession. There are certain things you can test and they have their physical dimensions and measurables, but after those things there’s really no way to know.
Now in the case of players like Jamie Collins, who can do a lot of things, there’s probably a little more wait-and-see to the approach. You can’t say definitively what he will do but you know he has all the boxes checked but you need to get him into the program to see what he excels at most.