Similarly. I have over 20 years of professional experience. I've worked on embedded systems, and with mainframes. I've done (amongst other things) kernel development, compiler (& RTL) development, line-of-business, mobile, server, and web. Code I've written has a MAU on the order of 1% of humanity. Ask me about being a "full stack" developer :).

I've seen a lot. But the more I see, the more I find to see.

The scare quotes are significant. Obviously nobody can ever see it all as taken in its most literal sense. But one can start to see enough that they can recognize the patterns.

If your job is dependent on the weather, one year might be rainy, one year might be drought, one year might be a flood, etc. You need to see them to understand them. But eventually you don't have to need to see the year where it is exceptionally rainy, but not to the point of flood, to be able to make good decisions around it. You can take what you learned in the earlier not-quite-so rainy year and what you learned during the flood year and extrapolate from that what the exceptionally rainy year entails. That is what levels up someone.

Much the same is true in software. For example, once you write a (well-written) automated test in Javascript and perhaps create something in Typescript, you also have a pretty good understanding of what Rocq is trying to do well enough to determine when it would be appropriate for you to use. It would no doubt take much, much longer to understand all of its minutia, but it is not knowledge of intimate details that "senior", "principle", etc. is looking for. It is about being able to draw on past experience to make well-reasoned choices going forward.