It is necessary to have a fundamental understanding, and often frameworks, as you said, can cast us to a single shape, making it difficult to see how else the problem could be solved.

But life is too short to always start at first-principles and rebuild civilization brick by brick.

Frameworks have three things: the code artifact: a Rails or a React, then the reified knowledge it abstracts: like how to structure a web application, and the community and their cultural knowledge.

Sometimes it makes sense to forego all of them and make it your own - especially when that layer of abstraction is core to the value you're creating and you want complete creative control over it. But often times they can be the difference between business success and failure.