Hey, I actually play Zilean and I think he is in an OK spot. He's probably better mid than support and shouldn't be picked into assassins with low CDs despite his ult. It's also not that good to pick him if your team lacks damage. Here's why I think he isn't in a bad spot for mid (although csing is super awkward until you get a lot of AP):
- RoA got a buff and he uses the item decently - the tankiness helps him stay alive without having to ult. himself most teamfights
- Morellonomicon is becoming a bit cheaper next patch and he often gets this
- high damage champs like Graves JG are more common than before and you can make up for their reduced tank stats.
I do agree that EVERY keystone is super odd on ZIlean though and it's a bit sad. He's just a weird champion and probably the only one in the game with only a single damage ability.
What do you consider to be his original problems? I think the only big problem is that he isn't very reliable due to all his damage being tied to a skillshot.
I also don't think his W makes that much sense now that I consider it more. What does it really do? It "rewinds" lowering non-ult. CDs. It's just a gimmick though because in reality, there is no decision making with it at all. You just always press W after using an ability to be able to use it again. For example, I want 2 Qs or 2 Es, then Q-W-Q or E-W-E. It's just automatic. They could do the same thing by making an additional cast of Q or E cost W's additional mana when cast immediately after. The whole W mechanic is just tedious and offers no real gameplay. It could all be made into a passive W and there would be no difference to the player.