Oh, now I'm confused. I misunderstood your previous message. I understood that you changed you mind and didn't want to add process_time_ns().
Can you elaborate why you consider that time.process_time_ns() is needed, but not the nanosecond flavor of os.times() nor resource.getrusage()? These functions use the same or similar clock, no?
Depending on platform, time.process_time() may be implemented with resource.getrusage(), os.times() or something else.