Those who are quick to jump on his mistakes are conveniently forgetting that he's been mentored under the defence non grata policy of Roberto.He's 22, he's still learning the art of defending i.e. when to press, when to drop off, when to tackle, when to row z it.
He's got the ability to read a game and is one of the best technical gifted defender's in Britain. Once his bread is buttered and he knows the game he'll be one of the best in the world
As you mention, once he's assured at the bread and butter aspects of defending (which I'm confident Pep will focus on), he'll be a top defender.
I truly understand why he'll most probably leave but I'm grown up enough to acknowledge that his departure will be almost certainly be a loss.
Those who are suggesting otherwise really need to think a little more objectively, and I 'd suggest that start by taking those blue tinted glasses off.