Regarding this video
There was a scene I had where the darker corners of the room never had enough detail/light for the denoiser to make sense out of those areas. I cranked up the lights to insane values and lowered the exposure and it helped a lot. However, now the scene is impossible to see in eevee/material preview mode. So it seems to me like this approach might be a hack completely outside of the box of the expectations of the Blender developers because I always thought the goal for Eevee and Cycles was to cooperate and look as close to each other as possible. But when following the advice from this video eevee becomes useless.