"Well, if the goal is for software running on the host CPU to know the time accurately, then it does matter. "

I'm sorry, this is just moving the goalposts.

You said "It can't achieve better-than-NTP results without disabling PCI power saving features and deep CPU sleep states."

This is flat wrong, as pointed out.

Now you are pedantically arguing that some NIC's that do PTP hardware timestamping might also use a feature that some operating systems might respect.

That's a very far cry from "It can't achieve better-than-NTP results without disabling PCI power saving features and deep CPU sleep states".

In most cases, people would just say "hey i was wrong about that but there are cases that i think matter where it falls down".