Programming is a wide field. In some tasks, I'm faster. In others, very slow. Give opportunity to do only the things I'm good (and pay me!) and happy I will. But... I need to do a lot of stuff I'm not good, or is unrelated to programming per se (I'm a solo startup) and sometimes is like the time is stopped...
I think there is some fuzzy logic going on here: If the majority are 1/10 developers (as the op asserts) and thus form the baseline x, aren't the 1/1 developers by definition 10x developers?
Its much worse than that in my experience. Some people won't be able to jump over hurdles no matter how hard they try. I'm like that for making a website look good (pre-boostrap). I'd eff around an entire week on swapping colors and changing pixels sizes.
I know people who are full-time developers who I would class as less than 1x