It is and I wonder what some people are expecting from signing a CB for £100 million. That includes Woodward who was the first to link us with such a move.
Obviously we can expect for a £100 million CB to improve our defense. But just like any CB we can expect mistakes. Especially in that player's first season, especially if deployed next to players who have been caught out plenty of times this season such as Bailly and Lindelof particularly early in the season for the latter. It wont be a case of us signing a CB who doesn't make any mistakes, because that player doesnt exist. So it'll be about how often and how costly those mistakes are.
For £100 million we have to be expecting that he's at his best in all the big matches and his mistakes are rarely on those occasions, or that he can somewhat make up for the mistakes ala. Ramos and score lots of goals or something.
I've only seen Koulibaly a little myself. From what I've seen of course he would improve us defensively. But I severely doubt it'll be anywhere near £100 million of improvement. Thats another Pogba and I doubt he'll be able to change games as often as having another Pogba would.