You can do a lot when your entire machine is built around getting data to the GPU, and when your developers are allowed to sink large amounts of effort to maxim

You can do a lot when your entire machine is built around getting data to the GPU, and when your developers are allowed to sink large amounts of effort to maximizing for a single GPU instead of all GPUs on the market. An Xbox One X has a GPU in it that's 40 compute units at 1172 MHz. That's pretty close to a Radeon RX 580, which is 36 compute units at 1257 MHz. You can't run the PC version of Forza at 4K with that kind of a card, but the One X pulls it off.