To preface this, I don’t think zed is unplayable, since his late game carry potential is still high if he reaches 3/4 items. Like vel’coz, he doesn’t flat out need damage buffs. His kit just needs adjustments to move away from his Kassadin-esque gameplay.

To understand his problems, we need to talk about how he got here.

Post durability patch, Zed fell off for a while since three WEQs could no longer kill a target which heavily nerfed his early laning and trading. He came back OP with the reworked Hydra during preseason, but Riot immediately nerfed hydra, while also nerfing Zed’s base damage for both Q and E. Coupled with the durability patch, his lethality build became borderline unplayable, which led to everyone using the nerfed yet still much stronger hydra build. Then in patch 13.20, Zed’s W nerf lowered his mid game potential since W max before E was no longer viable, while his early game potential has worsened with the electrocute nerf.

With a weak early game and poor midgame, Zed now capitalises entirely on his late game potential as seen from his highest played + highest winrate setup:

Teleport FirstSrike, get hydra asap Zed

I’d have assumed this is someone like syndra or viktor’s runepage.

With Magical Footwear (300g) + Future’s Market (150g) + FirstSrike (~200g), Zed now reaches Hydra at about the 9-10 minutes. The high waveclear makes his scaling much smoother given his easier wave management and thus roaming/splitting potential, so getting to buy it any earlier pays back in folds.

Absolute focus simply helps the hydra playstyle much more than Transcendence, as Zed never gets close unless his target is within execute range. Meanwhile Transcendence’s takedown CD refund rarely makes a difference, since by level 11 Zed’s Q/E are limited by energy costs instead of cooldowns.

TL;DR There’s no reason to play lethality Zed with ignite + electrocute when he can’t snowball off them, whereas FS+TP hydra rush lets him become a mobile orriana late game. The W nerf that targetted hydra built instead made Zed completely reliant on the item due to his worsening early game.