He can't run a second defensive summoner, can't build any defensive items until six slot (maybe a hourglass), and actually does less damage with his ultimate then non runglaive ez does. Throw in the horrid early game and the mid range distance and I just don't see how he is op. Granted if he gets to just sit there and tee off on you during teamfights then yes he is going to look broken as anything. But then again Viktor and azir left alone will do the same thing to an enemy team and they can actually win lane.
If the enemy team can pick any combination of mao, j4, Annie, ahri, and thresh then he will basically have no team fight ability. Really the only thing I dislike about ap ez is being forced to pick mao or hecarim top lane to lock him down when I prefer playing rumble, vlad, and ekko.
I see him as a good pick when the enemy has low cc or a weak laner in mid that can allow you to push up your spike. Was amused to watch two glaive ez's get smashed by a glaive gp and a glaive mf today.