IMHO, syntax is the easiest part. Semantics are the tricky part. One very clear example of this is how Svelte and React deal with async stuff.
The Svelte approach follows the handlebar approach of having semantics be represented by DSL constructs - which is a very reasonable approach IMHO.
The Suspense semantics are so far off left field that someone literally wrote a whole framework specifically in response to its complexity[0].
And that complexity permeates every language construct used within a React component. Why can't we call hooks from inside if statements? Aren't if statements just JS? If you have to bring up React's internal implementation to explain, that's no longer "just Javascript", it's also a healthy chunk of very React-specific knowledge that you need to be aware of.
Vue is another example that provides a successful story of a very large algorithmic migration from a reactive system to virtual dom with virtually no disruption to consumers, thanks to the abstraction provided by its DSL. In contrast, try telling my wife (who's learning about class components in her React course) that functional components and hooks "are just JS, what's the big deal", and see how far that takes you :)
[0] https://crank.js.org/blog/introducing-crank