Sony's low level APIs for PS4 and PS5 (it doesn't use GNM) is almost a direct mapping to the hardware with very little abstraction compared to Vulkan/DX12. Vulkan is still very high level compared to what's going on inside the driver. There's no point paying the cost of Vulkan's abstractions when half the point of a game console is to have a fixed hardware target, hence GNM.

It's basically same AMD GPU and you can compile SPIR-V into its machine code optimally without any kind of made up "I'm closer than close to the hardware" secrets. Compiler optimizations are done all the time (see Valve's aco and AMD's llvm based compiler).

Vulkan is more than adequate to handle things for the hardware on the API side so I don't buy the claim that they are somehow "closer than close" to be better.