I agree that omitting the type rarely, if ever, makes the code more readable.

But readability can easily matter less than other things over the course of one compile. This is why I think the best choice is demanding top level annotations for reasonably complete code (say, every commit) and not doing so before I can ask for the shape of something, or see that it outputs what I thought, or run my tests, or see what type errors I get elsewhere.

It might be marginally better to demand it by default and have a flag to disable the check. Demanding it always is more than marginally worse (which is not to say it's the end of the world - it's totally not).