I'm not sure. I would expect that mature, older companies would be using less exotic tech on average: PHP, Java, C#, etc. Newer companies would be more likel

I'm not sure. I would expect that mature, older companies would be using less exotic tech on average: PHP, Java, C#, etc. Newer companies would be more likely to be using something more niche I think. It newer companies are more volatile, it may be that when funding dries up, the new company folks may have less tech overlap with the mature, older companies. I suspect this would have been more of an issue in 2009 and 2020. It felt like it was much more common to ask developers to be full stack specialists a decade ago. These days most jobs seems to expect one to know multiple languages regardless of what you're doing. Keep in mind 10 years ago I was a recruiter, and now I'm a developer, so my perspective then & now use different lenses.