[implicit]

For what it's worth, I get the feeling that the reason TypeScript is growing so much complexity is not because the language designers expect you personally to use it all.

It's there primarily so that your development environment can give you accurate feedback when you're using your favourite JS libraries.

[thomasz]

Exactly. The <title> of typescriptlang.org is "javascript that scales". All those features in TypeScript exists to express common js idioms in terms of a static type system, which in turn enables stuff that makes programming in the large easier.