I suspect they don't really need GPU to render it. It is usually training what requires a lot of GPU, not evaluation. So the Nvidia requirement is only to sell more cards.
Don't know much about GPU performance though except random links I have found online which tell that GPU is 3-5 time faster for ML.
i9-7980XE: 1.3 teraflops
RTX 2060: 52 teraflops
So for i9 the number would be higher if fma operations used, no?
However, when we do have tensors, the GPU and CPU would both work to their full potential, and thus the flops comparison ought to be valid.