You have 6 players for 3 roles...
RCB - Mazz/Dalot
CB - De Ligt/Yoro
LCB - Martinez/Shaw
Having a 7th squad option at Maguire wages is just dumb. I'd get it if he was a net positive contributor, but being a body that plays defense isn't a good criteria. Heck ETH was picking Evans over him, that should tell you everything you need to know
You are clutching at straws.
Dalot hasn't played RCB. There's nothing to suggest he would be better than Mazraoui there, who's just a decent makeshift option there himself regardless, and not a long-term starter.
Not sure what De Ligt has done to deserve starting CCB spot, whereas Maguire will just be the "7th squad option". It's really not that difficult to understand why we are much better with Maguire at CCB instead, as there's plenty of evidence of that just in these first ~10 games under Amorim.
Yoro hasn't played CCB and it would be a luxury to play him there considering our current options, as he is the sole natural wide defender in the whole squad. Maguire/De Ligt cannot play there. Martínez and Lindelöf cannot either. It's all about the physical deficiencies for those 4. Mazraoui can be a decent rotational option there, like I said, but he's not an out-and-out CB either.
Shaw could be a great LCB but he's seemingly never fit. Martínez is only good in possession. When he has to defend, be it set pieces or large spaces on opposition transitions, I'm putting it lightly when I say he's a liability.
The more realistic CB hierarchy right now would probably look more like this:
LCB: Shaw first choice, but he's never fit, so Martínez first choice
CCB: Maguire first choice, De Ligt second choice
RCB: Yoro first choice, Mazraoui second choice
Evans has done surprisingly well as a wide defender against Villa, and I reckon Lindelöf could replicate that sort of performance too, but they're ideally back-ups at both WCB and CCB. If Kukonki makes his debut this season, he'll be a wide CB as well. He's got the perfect build for it.