Always think it's best to judge a player on League starts, given that they constitute our bread and butter. In the four seasons that he's been with us, he's never started more league games than he managed in his first year:
Year 1, 23
Year 2, 16
Year 3, 20
Year 4, 12 (can only make 14)
I think Guardiola improved him initially, but for whatever reason (injury/luck/confidence/ability) he has simply not kicked on, and it's now time to cut our losses and move him elsewhere. I doubt he will improve enough for us and we can no longer afford to play players who are 'okay' when paired with Laporte but drop off massively when paired with others.
I reckon he'll quite likely end up at Arsenal, where he'll form the base of Arteta's new defence.