WoW has always been CPU-limited in mass encounters and in general because it is only using one main cpu-thread. There is nothing they can do except switch to a newer engine or rework 18+ years of spaghetti code.
Again, see here for confirmation if you don’t believe me:
https://eu.forums.blizzard.com/de/wow/t/ruckeln-in-game/235972/7
Here is the DeepL translation:
Hello Neviz,
wait my cpu is so bad but actually it is never really used to capacity so between 20-30% max 40
WoW mainly uses one core and a few others with lower utilisation. The CPU load is then never 100% overall, but the CPU is still the proverbial performance bottleneck here. The fact that you experience stutters in instances and raids is not something you can fix with tips and tricks, but an upgrade of the CPU would bring a significant improvement in performance.
Maybe it helps you understand the problem here.
Except the X3D is about 30% faster in WoW because of the extra CPU-cache which helps alot in CPU-limited games.
See here:
https://www.pcgameshardware.de/World-of-Warcraft-Dragonflight-Spiel-73654/Specials/WoW-Dragonflight-Benchmarks-Anforderungen-1408516/2/
I never said the game performs great, especially if you don’t have a high-end CPU and even then you will have subpar FPS in many situations.
Here are some screenshots i took with 40-80+ players on screen, you can see the FPS in the bottom right:
Even though the average WoW player would say these FPS are really good and playable, the problem here is the bad framepacing with microstutters which makes it feel really bad.
This is mostly because of the addons but the underlying issue is that the one CPU-thread is choking on all these player inputs.
You don’t unless you want high refreshrates and 60+ FPS in a raid (not counting world events).
Most players, even most streamers on twitch have really low FPS (imho) in raids and M+ dungeons. Just zap through wow streams, you will find some showing their FPS and they are mostly in the 30-40s.
This is just hyperbole, if you want to be taken serious here don’t post something like that.
They have been selling it since 2004 
I had many CPUs in that timespan and it was always the same, if your CPU wasn’t up to date you had a bad experience in 20+ man raids and even some more complex dungeons later on like Freehold.
PS: here’s a bonus screenshot for you to better compare the FPS, my settings are on 7
and here with more people and the MSI Afterburner OSD, see the CPU usage, mostly one core (this is not all WoW obviously with stuff in the background like chrome etc):