Haha so why is he shit then? Stats not high enough? That would make him toxic, too much sustain. It has to be the mechanics of his kit.
He lacks:
A reliable movement ability
A way to boost movement speed
Built in Crits, %health damage, armor pen or significant magic damage
Built in resistances or a way to block, parry or reduce incoming damage
You won't find any other champion in the game that is lacking all of those things. Only Aatrox. He has the most bare bones kit in the game. The things he has, tons of champions have--a way to boost attack speed, a way to heal, a way to defy death...Volibear does that better and Zac makes enemy have to actively do things to stop his revive, which forces a choice in team fights.
It is his kit, so to say he doesnt need improvements on the things he is lacking is nonsense.