I hate the "champion X is weak to stuns" argument. Unless you're a tank or
, you are weak to stuns.
While a 49.1% win rate is lower than 50%, it's not by a significant amount. LeBlanc's kit was op with her silence and she maintained a 45% win rate. Miss Fortune has a 52.66% win rate, and she's considered one of the weaker ADC's in the game. Win rate is effected by many factors, including how freelo people think a champion is, how easy it is for their team to capitalize on what plays that champion makes, how OP they are, how weak the rest of their opponents are, how much risk vs rewards they have, etc. Zed is the 5th most popular champion in the game, and the most popular mid laner, with a 10.71% pick rate in the last month. Yes, that averages to more than one Zed per game (thank you normals). He's gotten a bunch of new fans, yet still maintains a 49.1% win rate? That's an indicator of being OP, not balanced. Zed's very low risk, high reward as well. good wave clear and poke early means he's less likely to lose lane. His ability to dive into the enemy team, do damage, and get out alive (often with minimal retaliation possible) is another indicator of high reward for little risk. Killing a back line champion, making a fight a 4v5 is also a great way to signal to your team to initiate.
I'm failing to see your point about win rates meaning he is fine. If anything, they imply the opposite.
PS: Hourglass counters many ultimates, not just Zed's.