Apparently, they just replaced Denuvo with a different DRM, which seems to have reduced performance somehow.

Digital Foundry covered it in this video: https://www.youtube.com/watch?v=N0TTbdff_vE

Looks like Capcom listened to the fan feedback and removed Enigma from RE4. Relevant thread on the Steam forums.

Finally, the game's PC performance no longer suffers due to crappy DRM implementations.