As someone that uses the language everyday, these are real quirks on the language, but they are not showstoppers. The benefits of using exactly the same language in front-end and back-end, with shared types and everything, largely offset the small quirks.

However sometimes I kinda miss some functional stuff that you can for example find in Scala or Rust, like pattern matching. Specifically, we've had experience using/developing an input validation library for the backend in Typescript (https://github.com/StrontiumJS/Framework/) that is composable and also returns the correct type in one go. We used a lot of try catches for that, but that makes validation slow. So we started using "maybe promises" which are similar to Scala's Futures with Success/Failure. But the fact you don't have pattern matching in Typescript like in Scala makes it a bit ugly.