His quality is not the issue! He improved beyond recognition under Pep, who declared he was the best defender in the world under him, and his passing was a big part of that. Fit and match sharp he's on another planet to Phil Jones and Chris Smalling, that's not the issue with the transfer - everything else is.
The fact he's injured as often as Kompany, the fact he turns 30 in September, he's showed signs of being on the decline, his game suits possession play where he can make a big difference in build up play, they're paying a premium price for an out of favour player.
A well run club of their means would be either throwing their weight, and money, around to sign Sule, or Marquinhos, or Varane, or Umtiti - a young, starting CB for one of the best sides in the world - or they'd be going after someone like Pavard, a kid with loads of potential who looks ready to fulfill it. Oh, and it'd be happening in May/June, not 3 days before the window closes.