So much of it is down to good old fashioned luck!
Look at the current “top 4”.
Brady was a 6th rounder, Favre was a second round pick, and a back up in Atlanta, Romo was undrafted, and when Manning went #1, it was 50/50 between him and Ryan Leaf!
Also Marino was the 6th qb taken in his draft, and Montana was I believe a round 3 pick..
Since 1970, only Bradshaw, Elway, Aikman and last year Manning have been super bowl winning #1 picks (not sure about Plunkett), and Bledsoe got a ring backing up Brady
Steve Young was undrafted in the NFL, but was in another league
(All this is from memory, and I’m sure someone will be only to happy to point out my errors!)