I think this is true for any group of engineers - some will be much more productive than others. That isn't because those engineers are better, or "10x" though,

I think this is true for any group of engineers - some will be much more productive than others. That isn't because those engineers are better, or "10x" though, it's simply because they're working on a problem they find interesting in an environment where they're thriving. The less productive people aren't enjoying the problem they're solving, or there's something about the company or team that isn't right for them. Most capable engineers have the potential to be "10x engineers" compared to their peers if they find a problem they're passionate about in a company that works well for them. The real unicorn engineers are the ones who are able to drop in to any team and be like that.