I don't disagree with anything you've said. I understand the need to take the opportunity to buy somebody that's perhaps not necessarily needed when it arises like this seemingly has if it makes you stronger, i'm just trying to look beyond that and wondering where or how he fits in.
I don't think he's good enough to be able to just say lets bring him in because he's available and we'll work it out later. that's something you only do for genuine world class talents. Maybe i'm wrong and he is that good, i'd be very happy if he was, i saw very little of him at Valencia so most of my opinion of him is based on the games i've seen him play for Porto a few years ago where i thought he was better than average but nothing spectacular. Hopefully he has progressed since then and is worth potentially upsetting the balance we currently in that position.
I just don't see it as black and white as he's an upgrade on MDM and he's younger therefore it's a no-brainer. There's more to consider than that. It's only as simple as that if he's coming in to do the same role, which he very clearly won't be doing. Assuming we let MDM go, or he takes a new role as emergency dm, can we keep 3 starting centre backs happy whilst also giving enough opportunities to what is widely considered to be one of the best young defenders in the game? It seems difficult to me, especially when everybody has been calling for Pellegrini to stop rotating our defence every game for the sake of it and labelled that as probably the main reason why we lost the league last year.