Holding was a promising defender and good on the ball, had some cracking games at the end of last season. The problem is for any defender playing for Arsenal eventually gets the better of you. It is a graveyard for CBs because Wenger isn't really interested in them and the way they play is almost designed to leave them constantly exposed.
Only Koscielny in recent years has really made a proper go of being consistently able to play well, because he's unnaturally good at stepping out and reading the game. But even he has numerous occasions of looking shambolic.