For the afficionados, there's an excellent paper titled "The neurobiological basis of narcolepsy" published in Nature Reviews Neuroscience which examines the relationship between orexin and sleep as it relates to narcolepsy patients: https://pmc.ncbi.nlm.nih.gov/articles/PMC6492289/

In narcolepsy type 1 (NT1), patients have severely diminished orexin levels. This appears to cause them to inappropriately enter REM sleep.

OP notes that the mutation lowering the sleep requirement causes an increase in orexin. I wonder whether the increased orexin could be inhibiting REM and perhaps facilitating a more restful architecture of sleep. Alternatively, perhaps elevated orexin levels during the day cause wakefulness such that you just don't need as much sleep, regardless of how efficient the sleep is.

It would be interesting to compare sleep tracking data of people with and without this mutation to see if there are significant differences in time spent in different sleep stages.