But our midfield hasn't been getting obliterated because 'Casemiro doesn't have a back up'. Our first choice midfield is what's taking the battering.
Sure, but it's quite likely he believes that's more an issue with early season form/gelling/fitness. Like last season. ETH has played this way (1 DM + 2 #8s/#10s) at Ajax and here last season. He bought Eriksen to be the 3rd player in the Case, Eriksen, Bruno midfield and people were saying the exact same stuff in the first games of last season.
I don't think he's going for Amrabat to be a starter, basically. He probably expects the current starters to improve their form. Amrabat is likely a Case cover as well as a plan B for games, when he wants more ball control in midfield.
PS. I think our biggest problem has been the midfield so far, but more so the attack. The current triplet is clueless and offers no goal threat. Yes we don't keep the ball, but I don't think he cares about the possession so much.