I can see the case for FOMO, as I felt that when I was a SWE. Now a UXE, I feel more at home with my ladder but my specific role is where I feel like the imposter. I'm aware of my potential and the feeling of being nimble, yet in my day-to-day work I feel sluggish. So seeing fast movers is where I struggle a bit.
Pick up a side project if you have time, join a time bound hackathon if you don't. That's what I did when I started feeling that way at Google, and about a year later I left because the company I was working on really needed me full time. If they didn't, I would've remained happy spending a few hours a week on it.