Native CPU instruction execution doesn't guarantee 1:1 throughput, let alone account for the fact that the PS5 has over double the raw power of a Steam Deck.

Translating API calls from the guest software to the host's equivalent isn't free, either. If the emulator uses hardware virtualization, you can also add the extra cycles spent every time the guest needs to perform a hypervisor call.

In a decade, maybe the IPC gains would be enough for something with fewer cores and lesser clock speeds to be able to do the equivalent work of a PS5. Right now? With a Steam Deck? Good luck running anything more intensive than an indie title at full speed.