It's much easier to see a mistake from a misplaced pass or missed interception than it is for the ones Ogbonna would typically make. For him it's usually down to his positioning or reading of an attacking phase. For this reason I disagree about his defensive 'smarts'. What he does have going for him is incredible athleticism and ability to recover a situation.
I've always said he would suit the Premier League more than he does Serie A, as these kind of errors are not exposed as much in contrast to the more physical game required, which he excels at. If you look at someone like Mamadou Sakho, I know a few Liverpool fans are pleased with him so far but for me Ogbonna is more complete as a defender and better with the ball, he's less brainless.
Really we should be looking to develop him as the modern game, Serie A included, has been heading towards a faster and more attacking game. He's a modern type of defender.