One of the best all-encompassing measures of a QB's greatness might be playoff wins. If you look at this stat against most lists of the greatest QBs of all time, (at least those of the Super Bowl era) it lines up pretty closely.
Only 11 QBs in history have more playoff wins than Patrick Mahomes, who already has 11 at age 27.
The list with more than Mahomes:
Brady - 35
Montana - 16
Manning, Young, Elway, Bradshaw - 14
Roethlisberger, Favre, Staubach - 13
Rodgers - 12
- Tom Brady has more than double what anyone else has, but at age 27 Brady only had 6 playoff wins.
- Joe Montana's 10th was the 1988 Super Bowl win over Cincinatti, he was 31 years old that day.
- Peyton Manning and John Elway both got their 10th at age 37. Brett Favre's 10th win came at age 32.
It already looks like a good bet that Mahomes will finish #2 all time in that measure. Everyone beyond 10 wins is a Hall of Famer or will be.