SAM also can have a far greater negative impact based on its tendency to put more load on the CPU too going by posts on reddit in the AMD subs. ReBAR is more conservative, Nvidia whitelist more games here and there but you can easily enable it for every game using Profile Inspector and it might yield a few more fps, it might not, but typically losing fps is not a thing when force enabling ReBAR.
Back on topic with RTX though, this is specifically RTX related as it involves Ray Reconstruction and how it handles shadows and finite details that would otherwise be missing in standard ray and path tracing. Some of these details are there in raster because these things are baked into the traditional probing of the scene, but can be lost with RT/PT due to the nature of denoising losing some of those details, and RR bringing them back whilst cleaning up denoising in the process.
I picked this scene by accident as I was walking past it on the way to a missiiong and noticed the strong green casting all over the place, a perfect scene to use to demonstrate Raster vs RT vs PT and Ray Reconstruction's benefits:
IMGsli:
https://imgsli.com/MjQ4MTM2/0/2
Pay special attention to the shadow of the tree on the ground. In raster they are blocky/messy and the motion is messy too.