Purdy is 4-2 in the Playoffs, taking his team to the NFC championship and the Superbowl. He got injured early in the NFC championship loss and lost in OT in the Super Bowl loss. He led the league in QB rating in 2023 and even last year, with nearly all of SF's offense injured, he was 7th in rating, ahead of guys like Mahomes and Hurts. He'll be 26 next year. And one of the smartest coaches in the NFL has hitched his wagon to Purdy. That should say pretty much all we need to know about him.
There is this ridiculous notion that there is some sort of "know it when you see it" level for elite QBs. During the 2023 season, people even on TD claimed Hurts wasn't an elite QB. Purdy has shown that he can get SF to the Super Bowl. His contract isn't that onerous - apparently, it's actually closer to 45m/year b/c of the 5th year extension included in his rookie contract.