Alright, I think the cull can be traced closely to relay streams pretty convincingly. Here's a few pieces of evidence.
1) Mio's Christmas relay
We all seemed to think that the event could be traced to something around the 24th of December. Well, Mio's Christmas relay happened then. It features the exact kind of conditions that causes bot classification (emote spam, constant moving to seemingly unrelated other videos/streams, etc.). We all know that HoloJP got hit hard, but not everybody seems to be hit. Here were the members that didn't participate in the relay:
Sora, AZKi, Choco, Okayu, Korone, Marine, Lamy, La+ and Iroha.
We also have the following pieces of evidence: Marine was able to host a 30k+ stream on Jan 1st since she hasn't streamed much. Okayu has been less impacted by the cull than most other holos. Korone's part of the Mikorone collab had much higher CCV than Miko's part (who did participate in the relay). But the most interesting person in this is Iroha.
2) Iroha didn't participate in the Christmas relay and her following streams took a little hit from her Median but weren't bad at all. As you can see she was still hitting 10k+ in a bunch of things, notably a Minecraft stream. But then Iroha made a mistake by participating in the Holox New Costume Relay. Her presence in the costume relay looked fine, but afterwards her CCVs tanked significantly, with Minecraft getting culled to 7k and then 3k after the relay.
3) Gura
Gura didn't participate in the JP relay but she participated in the EN one. And her CCVs dropped precipitously after the New Year relay.
This all seems to point at relay streams as being the main direct cause for Youtube to start mass labelling people as bots. And then these "bots" spread out to other parts of the vtuber and gaming worlds, poisoning everyone else slowly.
