In games where Sam has a league average amount of time before pressures he has a QB rating of 108. If that doesn't tell you that he has potential and that we've thus far squandered him i don't know what does.
Not elite protection.... not even good protection.... middle of the pack.
Surroundings matter an insane amount. Everyone in the world made excuses for Brady last year, saying that he had nothing to work with. His qb rating was almost the same as Sam's, and he easily had a better line a better run game, better play calling, and at least comparable receiving options..... oh and 20 years of learning under his belt. Yet he gets the excuses and the 22 year old with even worse surroundings gets dogged for similar levels of performance.
Put Mahomes and the Jets and he's mailing back that MVP. Heck we're probably having a similar discussion right now. I think he'd be a bit better here than Sam, but not much.