At the beginning of my career I worked in a team of 6 developers

I know few like that, had spell myself in my youth. Sadly, you learn in later life, you don't get compensated any more and worse, you set yourself up for burnout. Something I'm aware many did and, dare say, still do. Companies don't care, they'll take your blood but not good at giving it back or, indeed, slowing you down to the rate they pay you. Let alone, compensate for the efficiency (though that may have changed in the last decade or so in some places).

That's a good point. The fact is, if you are working for a corporation your salary is mostly dependant on your position and not on your output. Peoples outputs can be orders of magnitude different and they will still be earning roughly similar salaries. My advice to 10x-ers is: don't work for corporations. If you can be very productive you are selling yourself short.

I agree, I've found like 1 or 2 "10x" developers in my career. Before I met them I doubted they existed. I think that's why there's debate about whether they exist. It's a somewhat implausible idea and they're rare enough that plenty of people have never met one. However if you follow open source stuff at all it's relatively easy to find examples, e.g. in the Rust world Alex Crichton is an absolute machine. Probably a 20x developer.

Added to which, corporate bureaucracy often nullfies your impact anyway. That 10x potential matters little if the real hard work is tracking down the right person to reconfigure kubernetes or getting sign off to deploy to prod and the code writing is essentially all plumbing.

My question is ; if you somehow could level up all the other people on the team to the super productive person's level - how much more productive would the team have been? Clearly it would have been somewhat more productive but I think a lot of this "10x developer" stuff is kind of reductionist - the quality of the overall team being solely the total quality of each individual member. Sports teams are the obvious analogy here - with football/soccer you sometimes get these "team of the season" things where the best player in each position is chosen. One striker scored 50 goals for his team, another striker scored 48 goals somewhere else - wow, if they played together the team would have 98 goals. Except obviously not since there's a finite number of chances and the team is structured to play a certain way (often around their star player). And that's not taking into account ego/personality…

Same. In our team of 10 there was one guy that did about half the work. Making him literally the 10x (okay, 9x) programmer.

I find it interesting that this was early career. It lines up with my experience, too. Perhaps it's the case that, the less you know about a field, the more you attribute success to mysterious personal characteristics. And the more you know about it, the more you understand the role of circumstance and situational dynamics in determining performance.