Thanks for completely ignoring the point I was making.
My point was "he will come good" isn't a valid defence for a 25 year old centre half. He should have come good already. He's not a youth team player, he's not just starting out in his career. He's made nearly 250 first team appearances, spread out over 8 seasons. This isn't a youngster, it's an established first team footballer. He should be better than he is, and we can't be expecting him to improve hugely from what we currently see.
Saying a player isn't good enough for City isn't arrogance, it's an assessment of the current situation. We're a side looking to win domestic, and European, trophies, at the highest level. That means we need top quality players, Mangala hasn't performed at a level you'd expect from someone in a team like City often enough, he's too error prone, he's too clumsy, his positioning and decision making aren't where they need to be. He's not a bad footballer, far from it, but "not a bad footballer" isn't the level City are aiming for these days.