I've worked jobs with such a disparity. For a govt census job, the top two workers out of 20 visited 3x the dwellings per hour and had a ~4x success rate per dwelling compared to the average, so they were literally doing as much as the other 18 employees.

What were they doing differently? And why were the other workers not trained to do the same?

They've almost certainly been just nicer people who people liked to communicate better. Like, young pretty girls with pleasant voice. And they knew how to build right approach to people. That's it, and it can't be trained.

I do have a source, and I finally tracked it down:

https://nature.berkeley.edu/ucce50/ag-labor/7research/7calag...

I'd guess no matter the original context, once you're being 8x more effective than your colleagues, it's due to some kind of engineering. So in agriculture, your 8x hay mower is the one who's built himself a scythe instead of using a hand knife.

In that case, should he tell his employer he mechanized his work?