That’s the whole point about bad viral info, it’s hard to kill. That viral Reddit thread you linked further up was just a game of broken telephone that still pops-up now and again and people keep it alive.
TDLR, again, leave rtxgi_scale alone as it affects RT and NOT RT lighting too (as you pointed out).
You just confirmed what the dev said 6 months ago:
When you set rtxgi_scale to 0 that means that the baked rtxgi will also be off. While this will give you better framerate, and might be another reason for following the guides gives you better framerate, some levels that rely highly on this baked global illumination for their looks will become excessively dark as they will lack sufficient light contribution in heavily occluded areas. This is the reason why we decided to not support turning off Global Illumination from the settings menu as it makes some levels almost unplayable due to the darkness for which we have no suitable fallback.
The other dude gave you that bad viral info at first, which he later amended at least, when corrected.