Somebody has to come up with the intended results of the optimization for certain chips and the actual benchmarks in the first place. So they do write assembly and test various things.

However, that person probably have extensive experience in that narrow set of problems. Most programmers don't.

With the right feedback cycle with the appropriate debug counters, absolutely.

There are still jobs where you end up writing large amounts of asm regularly and this is absolutely table-stakes for that. Otherwise there would be no point using asm at all, you’d just use C or another high-level language.

There was once a case where someone dropped from asm to machine code to shave a little more performance off. Sometimes asm is too high-level.