I see it as a gradual thing. Early in the project loosey and then as the software matures add in more typing. But yeah, everyone needs to agree on the right level for that stage in the project.
You seem to be under the impression that types are for late stage development. I find them indispensable early on. First, because they let me feel out where my assumptions conflict, often before I've gotten to writing the bit of code that will make it obvious. Second, because when my assumptions are wrong, the type checker is a tremendous help refactoring - telling me all the places my old code is incompatible with my new assumptions. Both of these mean I don't need to be quite as sure that I've got things exactly right as I start coding.