I agree, I think it’s still really valuable to know about the html behavior that you might be overriding or extending with your framework. For example if you want to implement a form in react, it’s much easier to rely on native browser events and validation than to roll your own. Also the more you use browser native elements the better things are for SEO.

Basically the native HTML implementation is generally more stable, more accessible, and less error prone than trying to build the same thing in a framework.