I disagree with your last sentence. Tom Brady was a 6th round pick!
I have watched lengthy game clips from Brady's last year at Michigan.
He did not look like a potentially great quarterback in 1999.
A potential starter in the NFL? Maybe.
I think Brady completely transformed his game during his rookie NFL year.
His drop back speed, foot work, posture, arm strength, release, and accuracy showed dramatic improvement by 2001.
Hmm....12th? round draft choice vs. a 6th? As I recall there were 28 teams in 1972. I’ll agree that Brady was better than Sipe, but even in 1972, a 12th round pick was a very long shot to even make the team.
Now it’s only 7 plus a compensatory round.