I wouldn't call myself a 10x dev but at my last startup I was very productive, definitely more than expected at my skill level, because early on I had a lot of access to the people who designed our (undocumented, untested, and buggy) backend system. Then when I got a feature ticket (consisting of 3 words) I was able to quickly bang it out and deliver it, whereas other more senior engineers struggled because they didn't fully understand how the backend microservices actually worked and talked to each other.
Now I work at a big tech co and I'm in the latter position: I have a hard time understanding our complex CI/CD, and don't have nearly as much understanding of all the existing components. As a result I'm not nearly as productive and back to feeling like a 1x or 0.1x dev.