I think it's now fair to say Corki is the game's worst champion.
This is a X/post from reddit.
Preface: I'm ignoring Taliyah because she is still brand new and, even if she is genuinely undertuned, will either get buffed very soon or people will figure out how to play her.
I made this claim a couple patches ago--right after he received the nerf to the ratio on his auto attacks--but because it was a little premature at the time, I was mostly ignored.
Now, 3 patches later, at 6.10, he still sits at the bottom of win rates for both mid lane and ADC. The common argument is that win rates are not everything, and this is absolutely true. Let's say a champ actually is viable and quite strong. What would then cause this champ to have a low solo queue win rate?
Here are a few factors imo:
a) The champion is strong, but very difficult to play.
Personally, this explains why multiple hard to play champions tend to have lower win rates. Lee Sin, Kalista, Vayne, etc are all viewed as strong champions, but in general, they are just difficult to play at a high level. I also thinks this explains Syndra's lower win rate, too. Corki is NOT hard to play. He has a tricky to land skill shot, but aside from that, he is as simple as they come. You poke with your pokes, you all in with E on. You use W to escape. Only package plays require a little forethought and proper timing to execute correctly. On the whole though, Corki is a relatively simple champ to play. Yet, his win rate still sucks.
b) The champion is not designed for solo queue and works best in a competitive and more coordinated environment.
Kalista and Tahm both have very low solo queue win rates, but are still picked in competitive play. This is because they have unique strengths that benefit and are benefited by extreme coordination. What about Corki? His kit SCREAMS solo queue god. He has burst, has poke, has strong autos, has a great escape, and has potential great playmaking ability with the package. You can basically use the same descriptions for Ahri's strengths, minus the spammable hard CC, and not surprisingly, Ahri is a very strong solo queue champ. Yet, Corki, who shares most of the same characteristics, still loses more games than any other ADC and mid laner minus Taliyah and Mordekaiser (Mordekaiser, despite the perception of him being weak, actually has a 51% win rate top lane).
c) The champion is a strong niche pick, but does poorly in a general environment.
What is Corki's niche? In fact, he is very much defined as the ADC who deals mostly magic damage. It doesn't get more clear cut than that. Ideally, you would pick him bot lane if you have an all AD team comp in the rest of your roles. However, he is currently so weak, wouldn't you rather have Lucian with his current armor shredding build, or even someone like Kog? If anything, Kog probably does more magic damage than Corki.
d) The champion is undertuned and weak.
Bingo. Corki sucks.
He has great strengths on paper, but the damage on all of his abilities was nerfed, and then when Riot also took 9% worth of damage off all of his autos, that was the final nail in the coffin.
He is a champion who relies on his laning strength and mid game power spike to dominate and end games before he arrives at his weak late game. Problem now is, he does so little damage, he loses all trades and can't win lane against anyone. Thus, it's hard for him to hit his mid game power spike.
What's worse? His key item, Trinity Force, is getting reworked into a stronger on hit bruiser item, so that's another indirect nerf to him! Corki is a champ with essentially zero real utility. He only provides damage, so if his damage is weak, he just doesn't do anything. His all in is weak, his poke is laughable, and he can't really kite either because his attack speed is so slow.
Corki needs either a buff or another rework. Probably a rework because he is always either too strong or too weak, and so much of that strength tends to be tied to Trinity Force as an item. I feel that's unhealthy and clunky game design. At any rate, he is currently in the garbage pile and something needs to be done to bring him out of it.
Riot tends to over nerf a champ and then leave that champ sitting in their over nerfed state for too long. You can argue that Tahm is overnerfed too, but at least he brings enough unique utility to a team that he CAN be a strong niche pick. Corki is a generalist that currently sucks at everything. I dont' even play him, but I feel bad that he's left in the gutter like this.
An interesting fact: Look up op.gg's top Corki players in NA, EU, and KR. Every single Corki "main" has abandoned him (generally for Lucian). Is this not a problem? Even Illaoi and Mordekaiser have dedicated mains that stay true to their champs, and they are generally seen as really weak in the current meta.
tl;dr: Corki sucks hard, was completely overnerfed and needs either a buff or a rework. Don't leave champions in this state Riot!