Rawalanche:
I know quite a few folks from the high end studios you named, and I can assure you most of them don’t use AO as a separate pass they put on top of the renders. AO still has it’s place in form of a map/shader to mask out concave areas for procedural weathering effects, but that’s about it. No competent CG artist in this decade spends additional time and resources to render an additional pass used just to introduce a bias to their renders.
AO in UE4 is present because by default, and also historically, UE4 did not have any realtime GI solution. You have just solid ambient light color which you need to combine with AO to get at least remotely believable result. But if you have an actual accurate GI, which SSGI is, adding more AO will just give you worse results. And there’s nothing artistic about that.
You can clearly see that on the GIF posted above. You can see that SSGI at default setting still creates a lot more pronounced and detailed concave light falloff than SSAO. There’s no need to introduce any more AO on top of that, and you can also see that SSGI with AO set at 1.5 just burns concave shadows, making the light falloff appear lot less realistic.
That doesn’t mean that requirement of “deeper shadows” for artistic purpose is invalid, but that should be done on color grading level, after the rendered result. Not by doing ******** with light transport
Indeed, aren’t there custom surface biasing for lightbounces now? I know at least Renderman does it this way, and it’s still one of the most popular production renderers.