This is useful for some devs in some situations, but let's not go overboard. Teaching newbies to venerate vanilla is almost educational malpractice.
These days vanilla JS DOM APIs are pretty straightforward. It's well worth learning them and using them on small projects where a library like React is absurd overkill.
That's a false dichotomy. There is no such thing as an intrinsically good or bad language, and if the use of frameworks demonstrated the intrinsic flaws of a language, then all web-facing languages would be equally flawed, because no one avoids using frameworks in any of them.
Learning how to write "vanilla" JS (that term really bugs me) and how the DOM actually works is valuable regardless of whether the scale of most modern applications makes it efficient or cost effective to do so.