> although not with type check enabled (due to various limitations)

Curious what limitations there are on static type checking. It seems like a matter of your IDE setup

> My own experience is that the DX with "real" TypeScript is much, much better than JavaScript with JSDoc

I agree with the DX point. I would just point out that if you're using JSDoc and getting intellisense from it, you are using TypeScript

Not a limitation in language service, but an issue with the codebase itself -- legacy codebase with a lot of missing/incorrect typing from upstream JavaScript code (owned by other teams), making it practically impossible to actually run type check.