There are too many haters and stans in sports discourse now, so people are just trying to get their hot takes off. But the real answer is longevity. Lamar has 2x MVPs and 3x First-Team All Pros, so even if he does have a stinker slump he still has a 7-season resume of Tier 1 play to fall back on. The younger guys don't have that. Mahomes lowkey has been playing Tier-2 ball for the past few years but he has 5-seasons worth of goated play so he's pretty much untouchable. It is what it is. People are just too quick to give up on young QBs figuring it out, which is why they have these stupid whiplash takes where one game a guy is an elite future-goat and the next game he's a bum who should be benched. If social media was around back in the day these same guys would be saying the same stupid shyt about a ton of HOF QBs.
Purdy is on his 40th start with 70 TDs and 32 ints. At their 40th starts, Peyton Manning had 70 TDs and 52 ints, Brady had 57 TDs and 34 ints, Brees had 51 TDs and 37 ints, Roethlisberger had 50 TDs and 41 ints. Mahomes being a unicorn who dominated basically immediately has destroyed people's perception of normal QB development.