There isn’t a lot of evidence to back these claims up. For most users, it’s entirely transparent. You would never know a game shipped with Denuvo unless your first launch is offline and it fails to authenticate.
There have been games that had their performance impacted, but I don’t think it’s the norm. Games like Doom 2016 shipped with it and saw no performance gains when Denuvo was eventually patched out. I think titles like Rime and RE8 are usually the exception, but it’s something I always watch out for in reviews. If a game runs bad, I don’t buy it, regardless of the cause.
Denuvo has proven successful for 2 reasons:
It’s actually effective. Games go months or even years without a crack.
It’s nowhere near as draconian as what came before (TAGES, StarForce, SecuROM, etc). Most players aren’t even aware of its existence. They just buy these games on Steam and they work, which is why all the weeping and wailing and gnashing of teeth that goes on in these threads never accomplishes anything.