When I'm writing code that will be distributed to other devs, I feel type annotations make more sense because it helps document the libraries and there is less ambiguity about what a method will take. As with everything, "it depends"

That's true, but it can also add unnecessary constraints if done thoughtlessly.

E.g. if you require an input to be StringIO, instead of requiring an object that responds to "read".

Too often I see people add typing (be it with a project like this, or with is_a? or respond_to?) that makes assumptions about how the caller will want to use it, rather than state actual requirements.

That is why I prefer projects to be very deliberate and cautious about how they use types, and keep it to a minimum.