It's personal preference and in honestly it also not only depends on what HMD you are using, but will vary even between units of the same type.
Trial and error.
FD has tweaked gamma many times so far, and the most of the comments around it comes from the early CV1 or vive days, and the first few years the scale was way way off for those VR headsets.
This was mostly fixed after a few years.
Personally I find it near criminal when games that offer a gamma curve setting but no settings for brightness or contrast.
As for the roid scanner I'm certain FD has been working to make the good roids stand out less than they used to don't think there is or should be a magic gamma setting that makes these pop more.
Hey I'm Thor -
People call me Bob.
Rule 1: Pillage. Then burn.
Rule 2: No such thing as overkill, as long as there are reloads.