Proven by who and what proof? Because Denuvo is the only one outspoken about how it doesn't impact performance despite all evidence to the contrary and they provide no evidence of their own beyond claiming it doesnt. Then saying they'll prove it doesn't and then backing out of proving it.
https://www.resetera.com/threads/irdeto-backtracks-on-plans-...
DRM and anti-cheat aren't the same though. That link is talking about denuvo DRM, not denuvo anti-cheat. Also, just because one implementation impacts performance doesn't mean they all have to.
I'll believe it when Irdeto manages to provide any evidence amounting to more than "Just believe us".
Both the anti-tamper and anti-cheat affect performance and it's incredibly noticeable to anyone who isn't building a new bleeding-edge hardware PC every year or two.