I dunno, I think the Python interface is adequate. Not great, but gets the job done. I write almost all my Vim scripts in Python.
The other thing is that the Vim API you use in these other languages is pretty much Vimscript anyway.
For me, Vimscript is basically a normal imperative language in the general neighborhood of perl and shell... I agree it is more awkward to write than Python, particularly with escaping. But it's a decent DSL for configuring text editors, and Python isn't as much.
For example, I wrote a macro to split long Python function calls into multiple lines, and I could access a parsing function that I already wrote, along with Python's own compile() to detect when I've parsed a complete expression (yes, this one is Python-specific).
I also wrote a macro to submit the current file to a private pastebin, and AFAIK you can't make web requests with Vimscript.