Please tell when 6 of our 25 starters are UDFA's. Your 25% makes no sense at all.
I named 6 starters out of 25 starters; 11 each on O & D, and the K, P, Ls.
The six starters were: Gay, Vinatieri, Paxton, Neal, Ashworth and Andruzzi. 6/25 is approximately 25%... Que'll probleme?
I agree that as you go down the draft rounds the chances of making a hit decrease untill in the seventh round its probably 1-2% per choice.
But you forget that the UDFA are helped by shear numbers. If you sign 15-20 UDFA, and each has a probability of 2%, then the probability of finding one player, given that you have 15-20 chances, is the sum of the probabbilities and is 30-40%.
That overall success probability approaches the surety of a day one pick. Now as to whether the overall athletic ability approaches a day one pick, I doubt it. Most are slower or smaller, but not all. Some are just inexperienced; for example Neal is the athletic superior of most day one Guards. Others missed lots of college experience due to injury. Gay was such an example. A pair of late draftees are other examples; Patrick Pass was a highly sought recruit from HS; he was just usually banged up and had little or no production to show for the draft. So was Matt Cassel; he just sat behind a Heisman trophy winner or two.