Fable is still very much integrated with the runtime so there’s an expectation to handle those bullet points with inline annotations.
You can build an entire application in F# and compile to JS but another option is compiling to TS and calling that F# code from your TS app. I/O and views and whatnot are written in TS and the domain model is in F#. The entire model could be nothing but pure functions and resolve to a single expression!
1. Debugging can become quite a pain. Nobody likes debugging generated code.
2. You don't get to use libraries and tools from the enormous JavaScript ecosystem.
3. Eventually you'll find some web feature that they haven't wrapped in your language and then you're in for FFI pain.
In the end I found Typescript was good enough that it wasn't worth dealing with those issues.