As a fellow Googler, I sometimes feel similarly but I wouldn't call it imposter syndrome, more like FOMO. As a SWE I see all the tech non-Googlers use that I don't really get to use and the myriad of small projects people put out there. It's such a different scale.
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.