Displacement
Regarding your displacement, you can see the discussion here:
but more importantly, here:
Essentially, I think it is a bug that the gamma function acts on a the non-colour channel (displacement) in the PBR maps. Most PBRs come with a displacement map. If you want displacement, then you need to move the map out of the PBR channel, and into the actual Rhino Displacement map area; independent of the material.
Regardless, always make sure that the PBR has no displacement map if you want gamma and linear workflow to be switchable.
Gamma
Going against the norm, my recommendation for gamma and linear workflow… turn them both off, and leave them off. For everything.
They cause so many problems, and as we now both observe, the render queue is clearly not updating them “live” reliably. This way madness lies, as I have seen multiple instances where people are making lighting, material, and other adjustments, only for the entire process to be undermined by gamma & linear workflow (the banding you see here, for example).
My suggestion is to make sure that the raw render is always as “pure” as you can get it without the additional colour management of gamma & linear workflow infecting what you can see.
The implementation of Filmic in Rhino Cycles is also good for these types of scenes as a control, and while it does sometimes act a little extreme; doesn’t just bin up massive ranges of greyscales into the dark bands you see.
You can also probably use Photoshop (if you have it) and make colour adjustments on the raw render using OCIO management profiles, which are far more flexible.
If you don’t have Photoshop, then I can also recommend GIMP (which does have colour management) with the G’MIC extension, which has endless ways of doing colour transforms (not OCIO), and even film simulations.
bella
I know you are also a bella renderer user. bella will do OCIO natively, and you can load whatever profiles you need into it as you see fit. It also has lists of film simulation tone mappings.