How long do you need to wait for a stable environment to nerf a champion?

I have seen Riot comments acknowledging that Yasuo is currently too strong and they plan to nerf him. However, when this was first acknowledged over the summer, they also said that they did not want to nerf him until after Worlds because he was not causing in issues in pro play and that's where they wanted their attention. Fine, I understand this. But then after Worlds, we had the pre-season update and he wasn't touched due to so many new changes being brought in at once. It is now near the end of December and still nothing has been done to this champion. I am aware that an article went up recently in the News section confirming he will be receiving some changes in either patch 7.1 or 7.2 for sure (looking like it will be pushed to 7.2 as there is nothing for him in the current PBE cycle I don't think). My question is, why has this taken so long? I understand the game has been going through some major changes, I do. Yet Yasuo has not recieved any meaningful nerfs for several months if not a full year. How can a balance issue such as this, that the balance team is aware of, take so long to be dealt with?

I am sorry, I don't mean to sound rude but this is something that is really bothering me. It's frustrating to me that it can take so long before any sort of action is taken. Even Syndra and Lee Sin (and AP Kog'Maw for crying out loud) are getting nerfed before him and they only showed up on the radar around the time of Worlds.