Nobody can even state that it's actually happening "for competitive browsers" as even Chrome users are reporting an unexplained lag/slowdown. At this point, it's just wild speculation and bandwagoning.
I use a greasemonkey script for desktop and the Connect app on my phone to block instances. If I remember correctly, I think someone told me that instance blocking was coming in the .19 update.
My issue(I think) is a combination of games utilizing anticheat(I've not gotten a single one to work yet) and also trying to play non-new games that were not designed during the Steam push for compatibility. I can't use linux to play the games I like to play so I use a Win host for gaming and to run my linux install in a VM on the second screen.
I've got Grayjay on my phone but I very rarely watch YT on it so I've not really used it yet. Almost 100% of my watching happens on the PC and I've absolutely fallen in love with Freetube. No shorts spam, sponsorblock, more useful features on the player, it's pretty fantastic.
I don't think the issue is performance though. The unspoken part of this comparison is in bold:
"Linux vs Windows tested in 10 games. In the games we could find that work on linux, the performance was 17% faster on average. In all the rest of the games, Windows worked 100% better."
YT's push into ad-blocker blocking did the same for me that Reddit's API change did, that being it was enough of a push for me to stop using their platform. In Reddit's case, I get my fix from Lemmy and in YT's case, I use Freetube to watch videos. In both cases, I'm sure they're not losing money in my absence but I do feel better not giving them the data that I used to.
I also use FF solely and have no slowdowns on YT. I guess they like my copy of the browser.