And still the and miles ahaead of "user experience" than their competitor (they are pretty much unworkable for developers, it's insane how bad that ux is).
Looking back at 10 years AS 2/3 has brought us more than we have ever done within the Javascript era. The major lacking stabilities, compilers like TypeScript makes the modern toolset so incredible bad. Lovely to see as most of old AS programmers still approach these modern Javascript webapps way better than people started with Javascript without knowing the language behind it.
React is already typed with props. I see no added use for TypeScript. Yet another list of packages makes maintaining very hard and inconsistent (as types are declared in variant ways). Explicit (and simple) functions as React (e.g. hooks) provides won't need strongly typed code, less readability in my opinion.
If you're building a library / sdk, than Typescript comes in place and can make life easier for devs.