All this. And, no, they did not set up McCarthy to fail. If anything,. they went all in too much (on D anyway). They rebuilt the whole OLINE, they traded for Thielen and Mason. They drafted a WR in round three, and have two highly paid TEs.
It is the injury last year (and losing all that practice), not playing in the preseason, and the playcalling. I'm a KOC believer (still not sold on the GM), but he needs to adjust to the QB he has, and that's a rookie that literally didn't play last year at all.