If we don't want people to over-emphasize a bad performance to diminish a player, we shouldn't use a good one to do the opposite. Casemiro has been decent to good for us, yesterday he was really good, lets hope it continues. But your conclusion to downplay certain players is weak in my eyes. Midfield is about composition, put Bissouma next to a capable midfield partnership and he will be fine. Same for Ndidi. Put them in a badly balanced midfield and their weaknesses will look even worse. Lets hope that Casemiro isn't going to have the same trajectory that Matic had. We payed a lot of money for him even though he was already replaced by Real Madrid.
I am happy he is here but nobody can tell if a Bissouma could have played a good role for us as well, until lately it has been Eriksen, who really upped the teams level. And yesterday was a fantastic team effort, lets hope we can hold that level and this isn't another flash in the pan.