That depends on whether you consider 10x as to be a context-based quality or person-based quality, and IMHO the later is the thing normally discussed. A python dev might be 10x in python, but they'll drop to 0.1x when doing JS for e.g. the first month. Does that make them a 0.1x dev? I'd argue not.

New programmers on a team eventually affect the quality of the code as they work, and thus the project conditions. Project conditions can also include how easy it is to work with others on your team, which depends both on the new dev and the existing team. So that definition misses a lot.

Everything you said is true, but I didn't make up the definition :) This term was coined many years ago to highlight one simple idea.

That you can hire someone tomorrow that would have 10x the output of the average hire. Basically that such people exist.

Cross team productivity, and inter team dynamics are very interesting topics, perhaps more interesting, but this label for this topic is pretty clearly defined.

The meaning of 10x has blurred considerably - when coined, as far as I can tell, it seemed to mean that sometimes the most productive developer on a team is 10x more product than the least productive developer, not the “average hire“ - which is a very different claim.