I think about it like this: If I ask you to write assembler faster than what the compiler emits for one very specific CPU model, you'll pretty much always be a

I think about it like this: If I ask you to write assembler faster than what the compiler emits for one very specific CPU model, you'll pretty much always be able to do that (given enough time). But as CPUs become more complex, and compilers get better, achieving that win requires more and more "overfitting" to implementation details of the specific hardware, in ways that are not helpful or even counterproductive on older or newer models of the same CPU family. It's still worth it sometimes, of course. It's just more work and a lower value proposition on average.