Both are true. Lamar was let down by his receivers all day, but his play late in the game wasn't good. Dreadful ball placement on the INT, and really poor pocket awareness in the 4th quarter.
I will say though... do we think Mahomes and Lamar are equally as "clutch" as one another? Like Mahomes gets that treatment because Mahomes has lots and lots of game winning drives.
Or put another way... I don't think NFL teams are game-planning their offensive strategies, late in games, to avoid giving Lamar the ball back. Every single team in the league is doing that with Mahomes.
That's one of those spots where you expect your $50M QB to simply not make that mistake. An interception or fumble is literally the only thing he can't do there. Everything else is fine. There's worthy criticism for that.
