I disagree about externs being a waste of time for Haxe. I've written several, and they've been instrumental in helping me understand a codebase, and manage an upgrade process.

Haxe has a lot of metadata mechanisms that enable mapping language-specific semantics to Haxe standards (@:selfCall, and @:native for example). Haxe also has abstract types, which enable automatic inline runtime conversions (e.g., converting a native type to a standard Haxe type automatically depending on usage in haxe methods).

It's true you can't expect to find a high quality extern for a given version of any given library. However, it's pretty easy to write a small one for the subset of functionality that you require. It always ends up paying off for me.