I have maybe seen two people I would characterise as what other people might call a 10x developer. One of those 10x was truly someone who was worth 10 develope

I have maybe seen two people I would characterise as what other people might call a 10x developer. One of those 10x was truly someone who was worth 10 developers (at least!) given that not only was he capable of holding the entire business in his head, but he could also mentor and bring people together. At crunchtime he could also shield the rest of the team by churning out features at triple speed while still keeping them in a mostly maintainable fashion. He brought the best out in everyone. The other 10x was a silo of knowledge, was terrible at mentoring and wrote code which was neither readable nor high quality. That said, he was unmatched in his ability to ship and solve problems in distal regions of the codebase. In my evaluation of him, although he was 10x more productive than everyone else, I can't help but wonder how much less productive everyone was around him (and the team was larger than 10!). So tl;dr YMMV. They definitely exist, when they work right then probably can set up systems/organizations that can scale around them and generate tonnes of value. When they're egotistical/insecure vampires, their global value will be questionable but they will definitely look good relative to everyone else! I think moral of the story is don't hire assholes...