As I see it, you simply don't need pacy destroyers in a well-functioning compact possession team - no need to defend large gaps if the team is positioned well enough. Kante would be absolutely useless in this City team. What you need is a good 'regista' with centerhalf capabilities.
And I think players at top level cannot be both pacy destroyers and good controllers as they usually develop their strong points to overcome deficiencies. Though Rijkaard may disagree - he was both brilliant passer and athletic DM in one package. But can't remember anyone else - 'pivot' is a relatively new role, in pre-Cruyff and pre-Sacchi era teams weren't as compact as nowadays, so the position simply didn't exist in its modern interpretation.
Diawara? I started to watch Napoli regularly this season, but he's a reserve player that is rarely used. So, I'll refrain from judgement for now. Guess he befefits from Sarri's system a lot, it's difficult to say how good he would be under Pep. Many BM members rate him highly though.
Read somewhere that City were scouting Diawara at Bologna but decided to pass on him.