He might be great for Napoli but he might not be too clever here
He's rapid, great on the ball, vastly experienced, a leader and above all, bloody good defensively.
If Koulibaly fails here, any other CB would also likely fail and it will be indicative of failings/issues outside of the player base.
He's essentially everything that we need right now in a CB packaged together. Yes he's expensive and a bit older than we ideally would like, but he's the best option for us right now.