You seem stuck on the misunderstanding that they were covering for each other at some new level never seen in the world of football before. Maguire covered for Baillys mistakes and weaknesses, yes. Attempts were 8-13 so it’s not like it was the perfect game as you try to make out.
And you keep touting Lindelof's performances like he's a major reason of why we are defensively solid against big teams. Not the fact that we cede the majority of possession, play two defensive monster midfielders to shield the centre of the pitch and have 2 defensive monsters full backs. Our penalty box/area is tactically set up so that it has the most amount of protection for the full 90mins.
Has he performed well and deserves praise for those games? Yes, absolutely. Do we have to pretend that he's irreplaceable and be satisfied when anybody, who questions this is met with 'Lindelof has done xyz, therefore all the evidence points to the fact that he is flawless within that context'? No.
Against teams where we need to pinch the space and be on the front foot but not performed, we can absolutely blame the disjointed attack and perhaps to an extent midfield. However, let's not try to deflect the job of the
individual centre backs. In Maguire, we have someone, who likes to attack the ball, carry it forward, be aggressive on the defensive and offensive; of course we also see his flaws and the mistakes he's made.
Do we need someone, who can cover/compliment this and also be of an
individual quality
. Yes. Does Lindelof fit the former? Very loosely if you want to be generous (e.g retreating and not engaging regardless of whether it's Mbappe or Diagne is not a 'consistency' to be praising) but he is certainly not the latter.
Is Bailly the answer? Who knows. He hasn't been fit enough to really judge that. But let's stop touting that Lindelof is a fundamentally sound and all around solid defender when he is not. He's not easily replaceable in the context of the Utd squad because by default no one's been fit or stepped up but he is as average a defender as it gets in the premier league. Out of the back four, Maguire, Shaw and AWB are
easily a level or two above in defensive (effectivness) and all around general team play. They would be performing whether it was Bailly, Smalling or someone else. Lindelof does very little to elevate their performances.
One of the many general themes people talk about is 'playing the high line' with Bailly. What people mean is that very naturally Bailly will be higher up the pitch because he has that
ability to do that and with it comes the risk/rewards. Of course when you actually look at it, Ole doesn't really actively coach or set the team to play this way. That's not evidence to say that 'we don't play this way and therefore it's not conductive to how we should play because we've been successful with our super defensive performances against teams where we set up to counter attack'.
The truth is that we should be doing these actions anyways but Lindelof simply does not excel or engage in. We will rarely play a high line or be in an aggressive position in those situations with Lindelof because he's just not comfortable or able to do without overexposing himself. Smart because he knows his limitations but it is also one less option/weapon e.g just like AWB being poor on the ball and getting pressed i.e it negatively affects our ability to be on the front foot. It's not 'consistent' defending or 'good reading of the game'. It's extremely basic and we need to stop elevating this.