Ossoff > Sherrod Brown > Josh Shapiro (if he wins PA Gov, though I'm skeptical that he would accept) > Beshear > Jared Polis > Martin Heinrich > Brian Schatz > Pete Buttigieg
Sherrod Brown is both too old and more useful as an incumbent Senator. Shapiro is great but you don't go from little more than a year as governor to running for vice president. You're right that Buttigieg is bottom of the heap, though.
If Ryan loses in 2022, Brown can go for Veep and run for Brown seat in 2024 or run for Gov in 2026
Brown isn't too old when you have Harris
Agree Brown isn't too old. Yet that senate seat will be lost in 2024 if Brown doesn't run.