For me, it's definitely "a stand-in for "significantly more productive" with an unknown value". Neither the input nor the output can be properly quantified, and we don't really know the full set of variables to control for, and it inevitably runs into serious questions of inequality, SES, and background that are likely to make people even more cross.

I see it as more of a compliment. Nobody should be seriously and unironically calling themselves a 10x programmer, it should be bestowed by other people.