I think the opposite is true. The people who need to worry are those that know only the most popular technologies, for which documentation and examples are read

I think the opposite is true. The people who need to worry are those that know only the most popular technologies, for which documentation and examples are readily available. The people who know the stuff that's not written down anywhere are the ones who are safe. If all you do is crank out React code, you might want to start learning new things. If you know how to do RCE or are a networking wizard, on the other hand...