PBE: Base AD nerfed from 63-59
Do not underestimate such a change on a crit. ADC!
All Corki has is damage and most of it is short ranged as well as single target. His first few levels are already weak and he's quite item dependent. Unlike most mids, he contributes very little if behind. Anivia will still slow the enemy team, waveclear nearly instantly, manipulate terrain with her wall, stun enemies for picks, tank quite a bit of damage (her passive is great bait) etc.. Corki will merely throw some rockets while he remains at the mercy of his team (he requires a proper team comp. with peel and CC to be a good pick).
Corki was far too weak before 7.22 and he isn't actually out of line now. He was scoring ~46.5% in Diamond+ for quite a few patches. Since his strengths are very overt, his power is often blown out of proportion, just like for Ryze. Picks that aren't out of line in DIamond+ are almost never too strong in competitive either. People are just cocky and love to oversimplify things. For example, Ryze performs awfull in SQ and the same is true for his Worlds performance. He's incredibly overrrated, just like Corki was when he was supposedly too strong. There is also competitive inertia to some picks due to player investment, historic power, safety, reliability, well-rehearsed team strategies involving the pick etc. Lee was absolutely awful compared to other junglers at Worlds and yet he still saw play.
Corki is not over the top now in any ELO segment. As far as I'm aware, there's no objective/data-driven justification for a nerf and mere opinions (even those of very strong players) need to be supported by practical evidence. The community very often bandwagons on who is supposedly strong or weak and that level of group think tends to create a huge gap between expectations/assessments and actual balance realities. I still see people banning Yasuo today and talking about him like he's god tier when he's barely average even among skilled players.
It boggles the mind that Corki would even be on the radar rather than Malzahar, who has dominated for over 6 months at every level despite having quite low skill requirements. Corki's Diamond+ winrate is 51.5% and his late game winrate is ~48-50% (which is pathetic for an ADC and goes against the very reasons to pick him). Raw single target DPS does not automatically make Corki great late game. Most team fights are decided by CC, picks, AoE spells etc. An Anivia may not burst one target very effectively like Corki can if others provide CC, but if she can use her CC+AoE on 2-3 players for a bit, it's often more impactful for winning the teamfight. I'm not even suggesting that Anivia is necessarily OP but the point is that while Corki excels in 1v1 and small skirmishes, he tends to be much less useful in full teamfights. Corki is good late game in specific ways but he isn't dominant because he is very weak in other areas (AoE spells fall off hard, no CC, short range, somewhat squishy).
If Riot is indeed not trying to just rotate what's strong or define the meta, I need to understand the thought process here. Where is Corki's performance so out of line compared to other champions that there would be any merit for a nerf (especially one that affects him at all stages of the game)? I haven't even seen complaints about him and his banrate is basically nonexistent. I get that he benefited from the preseason changes but he wasn't the only one and doesn't seem to be anything out of the ordinary (indicating that he was overnerfed previously). You can't just suggest he might be sleeper OP on guesswork and then act upon it as if it's factual despite the evidence pointing to the contrary.
Corki's not even the type of champion who can ever really qualify as "sleeper" because he has been around a long time and has a good amount of competitive exposure. His pick-rate is decent and he has many experienced mains with years of experience. Moreover, his kit isn't exactly subtle. His strengths and weaknesses are both quite clear. He's not a Sona with fantastic auras that players may not appreciate in game (invisible power) or an Ivern with creative and undervalued uses of bushes.
He's pure damage and champions of this type tend to be the most overrated because it's easier to see the overt power rather than also think about what they lack and what they needed to get there (including good attack-move mechanics and battlefield awareness as opposed to the meme of just "right clicking"). When Anivia walls off a team from a critical area or slows an important target allowing a pick for a teamfight, people feel more like they made a mistake/got outplayed rather than understanding that Anivia's kit allowed capitalization in that scenario while Corki would not (and that can be a pretty large EV difference). The same goes if Anivia walls off an area saving her entire team after a risky Baron. People don't cry OP for that as much as if they get bursted through raw single target DPS but in fact that wall may have had an even greater value in the game. If Corki, or another champion like him, played lane perfectly, got a CS lead in a bad matchup and is now at a huge powerspike in damage, people are much more likely to complain about his damage rather than the Anivia situation. However, Corki deserves his strength just as much in that case even if people may be more bothered by it. **The alternative would be to add additional power elsewhere if taking away some of his raw damage (maybe make his normal W have a slow effect). I would have no problem with a 63-59 AD nerf if for example, his W could slow on tick from 5-25% (based on rank). I'd probably still prefer the AD over this situational effect on a skill maxed last but at least I'd consider this fair.**
BTW: His laning vs many picks feels much riskier now because Corki was one of the few mids running full MR glyphs instead of CDR/lvl. He also got mostly armor instead of base and scaling HP like the mids he faces.