Yep, left handed narrows it. And like you hint at, another big difference is FPS and RPG. FPS we don't have a lot of use for stacks of buttons. Even coop FPS - a little more time to think but not much.
But I also got a Corsair keyboard (with pretty lights, lol). It has six extra G keys and they're not a lot of use to me except Devving; opening programs. I didn't program the Corsair's G6 key -bottom left of the board- because in FPS I often hit it accidentally.
Maybe some day I'll get into RPGs... but presently a fancy keyboard is pretty useless for me. And even if I could use a many buttoned mouse, like you say, and you must be right handed - many buttons are mainly irritating.
I should have thought thru the important differences FPS and RPG, what hardware I need/ don't. Probably everyone's tried RPG style stuff online and got hammered by some mf with hardware keys, hot keys, several screens with inventory/maps, whereas most FPS shooters and especially me cba to fiddle with multiple buttons.
It's becoming Morlocks and Eloi. We're the pretty ones, but with skill.