The Serious Sam/Doom mods are outliers, they are probably not well optimized for NVIDIA (relying more on shaders than acceleration). We have numerous other tests that show a substantial hit to RDNA2/RDNA3 once Path Tracing is enabled anywhere. Desodre, 3DMark Ray Tracing Feature Test, Minecraft,
Quake 1, Quake 2,
Half Life 1. Even heavy RT does the same effect: Dying Light 2, Hitman 3, Lego Builder's Journey, Guardians of the Galaxy, Chernobylite, The Witcher 3, Ratchet and Clank .. etc.
But you might be right, NVIDIA invested into lots of optimizations for ReSTIR, RTXDI/RTXGI as well as various denoisers (denoisers are often a big chunk of the load). I am sure this helps. DLSS3.5 is going to be another big factor as well.