There used to be great Brits wrote:
You're giving ultra runners way too much credit. An 'elite level' ultra runner is basically just a hobby jogger who moved up distance because there was too much competition as shorter distances, The reason these stunt runners can break these records is because the current record holders are just slow, less talented runners like them. It's not like they are out there breaking 27 for the 10K. These are cheap "records."
You are right Don Ritchies 100k in 6:10:20h is slow.
That's why it got never beaten since 1978.
Did he post his Garmin data?