Really average in Ligue 1? Anyone telling you that is lying about being a regular Ligue 1 watcher, he is easily one of the best CBs in Ligue 1 and it was already the case with Reims, he helped Monaco fix their CB massive issues and has been by far their best defender.
Now, he is very much like Glik and isn't a "modern" CB, he is kind of versatile and has been effectively used as a fullback in emergency situations, which is something that I still struggle to accept because he doesn't look like a CB that should be able to defend wide but in Ligue 1 he can. He isn't really a passing CB nor is he particularly agile, for him it's all about his ability to read the situation and use his physicality. Imagine Maguire if he was able to defend when he is isolated.
I personally wouldn't sign him for United because the profile isn't correct but up to this point he isn't really average and hasn't been average in years. As an example he has been far better than Badiashile has ever been.