I have heard of first-hand stories where people interviewed and been asked to have experience in THIS particular framework. Despite the fact that the person had years of FE experience, worked with a similar framework, they were, eventually, rejected most likely due to the fact that they did not have experience with THIS particular framework.
So yeah, while I'm with you on the fundamentals, I'm also with you on the fact that it might not be the best approach if you want to stay employable.
Yeah, the issue is that those frameworks add their own paradigms and abstractions, almost to the point where you don't need to worry / know about the underlying core web standards.
However, this is also a missed opportunity, in that those standards haven't stood still. That is, a lot of web developers are stuck in 2015 and still use Angular / React, Bootstrap or some other framework, LESS/SCSS. Meanwhile in CSS there's things like oklch colours, advanced variables and selectors, layers, etc - I only learned about them recently while working with another developer who has in fact kept up with them.
That is, I'd argue that companies, designers, etc are being kept behind by sticking to these frameworks, because they can only design for and build in what those frameworks support, instead of what is now possible.
Likewise, React Native or other crossplatform app building toolkits, instead of truly understanding the underlying operating system and tools. For a lot of these same companies, things like widgets, live activities, watch apps etc are infeasible because their frameworks don't support them (or in the case of widgets, the frameworks take up all the memory budget). But I believe that if you want a great app experience for your end users, you gotta have dedicated app developers and -designers.
So yeah, while I'm with you on the fundamentals, I'm also with you on the fact that it might not be the best approach if you want to stay employable.