> Once you understand that, you can comfortably adapt to any new library/framework/whatchamacallit relatively quickly.

I disagree. If you know typescript, it's still quite a leap to be able to code with angular, and debug weird stuff where you stare at a blank page, and the back trace in the dev tools include not even a single line of code you wrote.

Also, the language isn't really enough. You need to be familiar with the tooling (npm/yarn, babel, whatever) to use most libraries; so unless you do everything from scratch, you have to deal at least with the churn of the toolchain.