There are more SBs won by 30+ year old QBs than 21-25 year old QBs... Most often the mental part of the game just isn't there for them and that takes time to develop.
The Lions keeping Goff isn't a bad decision. I'd wager Goff will outplay most if not all the rookie QBs picked this year. But keeping him at that $$ is crazy. Maybe this is their "shot" at a SB by keeping the continuity of the team, but you hamstrung yourself pretty heavily for the future.
But the premise that QBs on their rookie contract is the easiest way to win a SB is wrong. Few QBs on their rookie deal win a SB. Most that do are in their 4th or 5th year of the contract. I think Brady and Mahomes are pretty much the lone exceptions to that since 2000. And more 1st round QBs are busts than hits.
The trick is knowing which QBs have gone past their peak (26-32) and really can't lead you to the SB anymore. It was at that point I switched from holding onto Rodgers to trading him. The Vikings were smart (or lucky?) to move on from Cousins. Cousins could win one with the right supporting staff, but that supporting staff isn't in MN right now. Goff reminds me of a younger Cousins a bit. Not the elite, but the very good. He will win you a few games and keep you in others, but isn't the Mahomes, Brady, Rodgers, etc... level.