i don't know if this is true or whether people believe this. if you ask other people, they would tell you that sql is a very important skill to learn. i call bs though, like you.
sql is a common interview question, like joining and transformation etc. if its so simple maybe they shouldn't be asking this.
I don't see the contradiction. Something can be both very important and not that difficult to learn and not known by a plurality of interviewees. People ask (and fail) fizz-buzz and that's hardly difficult.
All of these foundation concepts are vocabulary.
We need vocabulary in order to understand and have reasonable conversations.
Do you need to be an expert? Probably not .. but yes, we should all understand.
I think we'll develop personal moats automatically. Some people don't are naturally uninquisitive. They'll be most at risk.