That’s exactly what he’s saying. He claims nothing has changed on the backend - by which he is referring specifically to anything that might have anything to do with performance related settings, issues, and so on. I don’t think he’s prone to lying about that.
As for what it might be, hard to say. Tons of external factors in an OS can come into play, very difficult for anyone not sitting in front of your PC to determine what the issue might be. Keep in mind that Windows itself can be your enemy.
This was claimed to have been “fixed” but… it’s Microsoft we are talking about here. Other than that, drivers, weird programs you may have recently installed, browser open with a bajillion tabs, the list goes on. My advice - crack open task manager and start playing whack-a-mole.
It can work with hyperthreading and has for some people.
[Tool] Core Switcher - Force GD to use all cores equally!
…the only way to determine if it works for you is to try it tho - manual steps are detailed that you can try first without needing to download anything.