I believe it. As a JJ McCarthy bobo, I've listed some excuses for him (became a father, it's just his first year, flukey schedule early on) but not staying healthy is a big concern, either way. There are always going to be different personnel and scheme to learn from week to week. So that's not necessarily a great excuse to me. If Brosmer shows anything next week, I think McCarthy is assigned the clipboard and the bench.
There is a TikTok guy who always comes out with the five worst NFL plays of the week, stuff like that, and this week it was McCarthy's five worst passes. The whole bit is that every play on the list is not from the whole league, but from the same player. There are also 'honorable mention' plays which extends the list to like 7 or 8 and makes it funnier (except when it's your guy, not so funny). Anyway, when you look at all the bad decisions and bumbling plays McCarthy made this week, and you see these all in succession, it's very persuasive. Does not paint a pretty picture. And I don't think this was the first time McCarthy was the feature player for this guys' TikToks. (I think Week 1 it was CJ Stroud but it could have been McCarthy if not for the 4th quarter comeback)
It's fun to make jokes during the game about how bad he is, and, it's way too early to give up on him. Maybe he needs one more offseason to reset. Like nicksaviking said, I think the most likely scenario is McCarthy does eventually find himself but with a different team. I could see him a couple years from now, coming in the second half for some team and throwing for 3 TDs and putting himself on the map again.
Unfortunately for us today, he is a long ways away from that consistency or competency.