> Duck typing is one of the best things about Python.

And duck typing with the expected contract made explicit and subject to static verification (and IDE hinting, etc.) is one of the best things about Python typing.

> If we ended up with a largely bug free production system then it might be worth it, but, just like other truly strongly typed languages, that doesn't happen

I find I end up at any given level of bug freeness with less effort and time with Python-with-types than Python-without-types (but I also like that typing being optional means that its very easy to toss out exploratory code before settling on how something new should work.)