Everyone who could compete with Zed was nerfed into the ground. Mana nerfs are the most egregious example.
Zed was never bad per se, he just never shined this brightly before, because there were a bunch of mages who could compete with him in the laning phase. Mana gating not being as bad to deal with, meant you could trade abilities with Zed. Being able to hit him with more than 3 spells before being OOM made his MR worth less, and made him less hard to push around.
Post mana-nerfs, Zed gets a hexdrinker, and a little lifesteal, absorbs your spells like they're nothing, pokes you with a million shurikens and then all-ins you, under your tower, with his absurdly safe ult.
Jungle ganks are pointless, because unless the Zed player is completely retarded, he can just shadow off.