I found the TypeScript contributors very responsive on GitHub issues. Maybe I'm just lucky?

I just submitted a bug[0] on Jan 5 and it got fixed on Jan 9.

Another bug[1] from a couple years ago was submitted Aug 4 and fixed Aug 5.

I'm pretty satisfied ;)

[0]: https://github.com/Microsoft/TypeScript/issues/21031

[1]: https://github.com/Microsoft/TypeScript/issues/4155