I think he is saying that CPUs and GPUs are generalized computational mechanisms. They have increasingly complex overhead that attempt to optimize general probl

I think he is saying that CPUs and GPUs are generalized computational mechanisms. They have increasingly complex overhead that attempt to optimize general problems. By limiting the context of use, specialized hardware can perform better than CPU/GPU. I think his thinking relates strongly to ASIC crypto mining hardware https://en.bitcoin.it/wiki/ASIC https://en.bitcoin.it/wiki/ASIC . "bare metal" is just a shorthand for the level of access to hardware that does not require a kernel/OS.