Thats not how football works. You can't give a team talk that says "everyone just worry about yourself" and think that you will get a good team performance from that.
Football at the elite level these days is a team game and any weakness in defence or attack can manifest issues in a completely different part of the pitch. Theres a reason Liverpool can play with fullbacks who can't really defend, they are usually on the front foot most of the game and defend from the front so TAA and Robertson aren't being asked to be positionally sound and the defensive unit isn't under a huge amount of pressure the whole time.
If United can get back to winning ways, suddenly people will think that the defence has magically improved and Maguire has got a lot better. If our midfield and attack protects the defence more they will find their job much easier and simpler.
This is one of the reasons I am looking forward to United under ETH. Hes a coach that priorities the team and system over the individual. Almost all the best teams are the same now. Everyone looks better in a good system. Players who come in find it easier to adapt. Substitutions to the first XI due to injuries find it easier as they have been coached to fit into a tight knit unit rather than a loosely coupled set of individuals.
I didn’t say players work in silos.
He needs to prove he can consistently defend at a top level first & foremost. If he continues to put on poor defensive displays him playing short passes to an FdJ or an Eriksen is something another defender can offer. You also miss the point that Liverpool can play with such attacking fullbacks because their centre backs can. . . defend well when required [mostly].
I agree that a more coherent midfield will in effect help the defence because we’ll have the ball more, it’s part of the reason EtH is going for players who do better in possession than out of it.
Put it like this. If you were joining an employer & all people could say was how much your colleague will improve working with you, then you asked how you’ll benefit working with them & the answer you get is, “well we’re unsure if they can do their main job correctly but you’ll cover some of their other deficiencies so get on with it’ how would that make you feel about said colleague? Every Summer he’s been here we hear the same ‘x player will improve things for Maguire because. . .’ but as you say it’s a team game, so what does he do to free FdJ up? or an Eriksen? or a Tyrell type at fullback? Can they look at him & say I can afford to try something here because he has my back. . . That’s why I’m more concerned with his defending than anything else, because if he continues to defend poorly nothing else will matter.