You seem incredibly overfascinated by shooting percentages. He also grabbed 20 rebounds for the second time this season, 1 off his career high. He controleld turnovers and he stayed out of foul trouble in a game where the refs would naturally have been looking for him, and played more than 40 minues for only the 3rd time in his career.
Big kid did fine. The shooting percentage is why he gets a B-. If he shoots well as well, he is looking at something in the A range.
The thing is that you don't get wins and losses based on rebounds. You get them on points and his shooting and use of the teams possessions was pretty dreadful. You seem to be giving a lot of credit to him for being on the court and staying out of foul trouble. Those aren't things that lead to wins unless you shoot a good percentage, play great defense or at very least make your free throws. Cousins did none of those things. He does rebound like a mad man and if my opinion that is what would have kept him out of the F range.
The Kings had many problems against the Clips (injuries among the biggest) but the "big kid" hurt you more than he helped you.