For me, even stereo adds very little over mono when it comes to music. For movies 5.1 seems quite sufficient. As for gaming, every tiny improvement they can make is something I'd be interested in.
Amir over at ASR [1] tests single speakers and then will often do a short subjective listen at the end of his reviews. Sometimes he'll mention how enjoyable a single speaker can be and fill the room with music. For myself, I'm rarely in 'the sweet spot' and so most stereo effect is pretty much lost on me anyways. So yeah, I'd agree that there is very much a diminishing return the more channels you add.
For gaming, stereo headphones seem to be best, imo. I've had the same pair of Crossfade LPs for several years, and they give great (as far as I can tell) spatial awareness in games, without any special features.
[1] https://www.audiosciencereview.com/