In terms of scalability, you may have different toggles based on different strengths of your system.
Great GPU? Toggle up the resolution.
Great storage I/O? Toggle up on the asset streaming.
Framerate could potentially be bound by any of these factors at different points.
What I think is a key validation for PS5, is that it does seem to confirm the idea of storage IO and data throughput as
a key performance factor in visual fidelity and performance next-gen.
You think Sweeney team picked PS5 because of what other reason? Sony must've worked with them.
In comments to Verge, Epic said they had been working more closely with Sony on the tech for Nanite. I guess there was mutual interest in exploring data throughput in rendering, and obviously it gives Sony a good showcase. It seemed more like a technical coming together than a marketing one.
Whether there was anything beyond that in choosing PS5 as the showcase system, I don't know. There may also be a marketing component here. It's possible also, though, that the data throughput on PS5 makes it as good a candidate as any other to show off the tech, even if they could have got a better GPU elsewhere. I think the key in this demo was the step-change in virtualised asset streaming and throughput more than raw pixel count, and maybe that stuff is just running better on PS5 at the moment if it's heavy on IO (pending optimisation etc).
