That's my point, can someone in that group instead of devoting more time than the average to their academic work take that extra time and devote it to their job?

No. If you plan to be successful, there is little to no time outside of being a PhD student. If you want to be in the top 1%, and especially the top 0.01%, you should plan to spend your free time researching to become an expert in your field. But such numerical distinctions are typically meaningless since, by virtue of working towards a dissertation, you should be pushing the boundaries of your field of knowledge and thus have few exact comparables as peers.

Source: me (several years now complete w/ PhD), my cohort in my program, and my PhD-earning friends outside my field.

Take olympic athletes. There are differences not only in the level of work but also physiologically between those who win gold medals and those who can't be olympic athletes. If you're a would-be gold medalist why isn't it possible to settle for getting into the olympics and have a job on the side?

That's an interesting analogy. If you can find recorded examples of part-time Olympic athletes from a competitive country that would help your point. By a competitive country, I mean one with non-negligible chance of getting a medal in that sport.

I wonder if they exist and if so, how rare.

I suspect it's extremely rare or non-existent for an athlete who holds another full-time job up to the selection time to get selected into a US Olympic swimming team, for example.

So if you had the capability to be one of the greatest PhD students in the world your strategy would be "do a bunch of stuff average instead"? How would you achieve such a high level of performance in the first place? Being a good grad student is as much learned and practiced as any other skill.

Being quite good at two things can sometimes be much more advantageous than being top notch at just one thing.

Scott Adams offered this as “Career Advice” (http://dilbertblog.typepad.com/the_dilbert_blog/2007/07/care...) in July of 2007:

"But if you want something extraordinary, you have two paths:

1. Become the best at one specific thing.

2. Become very good (top 25%) at two or more things.

The first strategy is difficult to the point of near impossibility. Few people will ever play in the NBA or make a platinum album. I don’t recommend anyone even try.

The second strategy is fairly easy. Everyone has at least a few areas in which they could be in the top 25% with some effort."

See also https://www.skmurphy.com/blog/2010/04/18/jack-of-all-trades/ for an exploration of how deep knowledge of multiple domains enables opportunities for knowledge brokerage.