uBO has the most people working on providing fixes though, and they get them out pretty fast. I've never ran into a situation where I couldn't get YouTube working again by clearing my filter cache so far.

It's perfectly fine and valid to question the pile of JS code executing in Youtube webpages, but in this specific instance the performance issues are caused by ABP/AdBlock. The issue has been acknowledged by the developers[1]. It affects only the latest version of both blockers, not previous versions, so it makes no sense to keep speculating Google is at the root of that specific issue.

Out of curiosity I investigated these performance issues myself using profiling sessions[2] and the faulty code is definitely in the latest versions of these extensions.

* * *

[1] https://gitlab.com/adblockinc/ext/adblockplus/adblockplusui/...

[2] https://twitter.com/gorhill/status/1746543688975581604