Brady won with less talent for his entire career outside of 2007.
A players "prime" is subjective and has nothing to do with age or how long they play. Mahomes was favored to win the SB and I believe 2nd in MVP voting when Tom was on the Bucs. This game manager part of him didn't exist only because he still had Tyreek Hill. You're cant sit here and pretend that 2020 Pat is a lesser QB than the one that's playing now.
More
Brady had Edelman, Gronk, Hernandez, Moss, Welker, Evans, Godwin, AB, Corey Dillon, Fournette...
Mahomes had Reek, Kelce, Hunt (kicked off the team before the playoffs), Watkins, Juju, MVS, Toney, Moore, Hardman, CEH, Pacheco...
Brady's way more offensive talent than Mahomes has had plus the Pats always had a top tier defense. His first three rings they were ranked 1st, 3rd, and 6th.
Prime isn't subjective. No QB has the game figured out year one. You think Stroud doesn't have a ton of things to learn? No matter how hot a QB is at the start of their career they still aren't finished products.
Mahomes is absolutely better now than 2020. He doesn't force throws. His decisions are quicker. His mechanics are better. He reads defensives better. He manipulates defenders with his eyes.
They had more explosive plays last year without Reek than they did with him. Stop looking at just numbers and pay attention to nuance. If you did you'd understand it takes years to hit your prime.