It's a valid point that we don't know how Varane will take to the PL, particularly with regard to rough-housing and aerial 'bombardment' (although teams don't really do that anymore relative to what it used to be like), but he has so many pros to his game and perhaps the biggest of all, above his ability, is he has played in an almost suicidally high line for years now. He has the pace, intelligence and composure to sweep up behind Maguire and afford him more peace of mind than anyone else we have at the club to go off and try and be whatever it is Maguire tries to be out there. I'm not trying to be harsh on Maguire here, btw, rather, he can fully commit to being whatever type of player he perceives himself to be with Varane beside him and not have to have one eye on his CB partner and one on the game he wants to play like he currently does.
Maguire is obviously no Rio or Vidic, but the comparison I'm making here is that, once Vidic arrived, Rio no longer had to babysit the backline, rather he could marshall it and instruct the pieces to go where he wanted them to go rather than having the anxiousness that a mistake or mishap was just around the corner, like he had pre-Vidic. So by Vidic arriving, Rio was released to go and be the player he wanted to be rather than the one he had to be in a coddled backline. This is what a 'tier 1' defender should enable his partner to do and where we can drag this back to the here and now and consider how much a player like Varane could transform our backline. It's not just his ability and individual quality you're buying, but the assurance to a partner and a backline as a whole as the flanker on his side also has a different remit with him there due to his pace and ability to cover without a moment of hesitation.
The Varane of c. 2018 was seen as dead cert all-time great and even with his mistakes and errors since then, he still has time on his side to get back to, or even go beyond, the level he was once at. There aren't many CB's on the planet who that kind of thing can be said about and it's a total no-brainer to sign this calibre of CB if there's a chance to do so.
I can't really talk about his development or lack thereof because, where I once intently followed his career trajectory, I haven't done for a while now, so perhaps
@JPRouve or the Madridistas here can give some insight into what's caused the deviation from what was looking like a straight line to the very top of the CB tree just a few years back. Varane, as is, with the mistakes and odd bad game he has in him is still so much better than what we've got here that it's not even funny.
Us tutting and sighing at the bad games Varane has wouldn't be much different to how Liverpool supporters would be with Van Dijk - you really wouldn't hesitate to take that kind of rough with the smooth compared to the game-by-game woes we currently experience with what we've got here.
I don't think anything will come of this, but if there's legs to Varane having an interest in coming here, I'd like to think we'd be willing to pull up trees to make it happen because: 1) 'Tier 1' already established at a top level club CB's are extremely rare to find on an open market - these guys get locked to contracts until they are physically shot, want away or are usurped by the next prodigious talent. One moving in what could be considered his prime years is a really big deal; 2) Our backline badly needs a player of his profile for the reasons given in the first paragraph; 3) he's a player who you can genuinely say has the potential to legitimately be considered transformative as the backline can then play as high as it wants and suffocate the opposing forwards; the midfield can take themselves higher up as a block, again causing applied pressure to opposing midfields earlier, which, in theory should lead to more turnovers and reworking of the ball to the forward line.