> And I can guarantee using a more sound (and more complex) type system like Elm or Rust would have never succeeded
Both Rust and Elm have a much simpler type system than TS.
Well, for Rust it can maybe be argued to have its complexities but Elm is dead simple. In fact the most common criticism of Elm is that it it lacks more complex features that people from the Haskell world are used to.
Allowing for the gradual typing of a dynamic language like JS is extremely challenging requiring stuff like structural typing which is not at all common in most mainstream programming languages. I don't thing there are many mainstream languages that have a more complex type system.
The value TS offers is ease of gradual adoption and access to the huge JS-ecosystem and for that you absolutely pay a price in complexity. It is absolutely trivial to design a language with a much simpler, sound type system that offers higher productivity and a smaller learning curve than TS but that wouldn't have much value for most people as the access to the JS stuff and gradual adoption.