This video might paint a bit too broad of a brush stroke in describing aces which is indeed more than just a tonemapper but it does highlight some interesting things that epic could definitely offer.
Yes the acesCG color gamut can encompass just about anything. But your display cannot, and so you do need something that translates the very wide set of values the acesCG color gamut encompasses and the range your screen can display.
That’s where tonemappers come in and this video is right about one thing, the aces tonemapper kinda sucks in games and cg applications and it is tucked in the engine in ways that are kind of annoying to suss out. Also if you don’t use the aces tonemapper and you just go from your acesCG working space to some kind of default sRGB or rec709 output your ocio config has on offer that also kinda sucks since it’s not a purposeful color transformation to get your acesCG colors onto your scene.
The other reason this really matters that may not seem as obvious is when you are lighting and developing your scene, if you don’t have a good tonemapper then you are constatnly developing lighting in a sort of uphill battle if that makes sense.
I’ve tried the “ultra realistic tonemapper” on offer in the video it’s really really nice and it does yield vastly different results than the tonemappers unreal has on offer. Not only has it convinced me that the one on offer in the video is better it’s also convinced me that there should really be more options to pick from as it really can set the visual tone in ways that are quite profound despite seeming initially subtle.
There is also the Khronos PBR Neutral tone mapper out there which I’d really like to get to work in unreal, but I can’t get the config file to work. Apparently it’s quite nice in blender and the interactive examples they have on their blog look convincing to me.