It’s very difficult to get good playoff production with a QB on their rookie deal unless you have a great team. SF was in the SB just a few years ago with Jimmy G so they clearly have a team where their QB isn’t having to carry them but it caught up with them in the SB against a team with a great QB. It likely will catch up with them again if Purdy faces Lamar Jackson. SF had a great roster before Purdy, which is why Jimmy G had success. He went to a team that didn’t have a great roster and got benched.
The advantage of not having to pay a top tier QB 40-50M is you can spend more
in other area's to build a great roster, especially with a competent GM
The disadvantage is you probably don't have a great QB in a QB league.
If you do get good or great QB play from a FA or a rookie with a roster like SF's, it's very dangerous.
SF got pretty good production from Jimmy G and great production from Purdy for 1M.
SF will crush the AFC in the SB, IMO