The risk you describe is real, but good testing coverage lowers it in a way that I find way more efficient than static type checking. When I have that good cove

The risk you describe is real, but good testing coverage lowers it in a way that I find way more efficient than static type checking. When I have that good coverage - which for me means the full pyramid of testing, not just unit tests - I almost never find that problem. Refactoring when you change your understanding of the domain can be a lot of work also when you have dynamic typing and lots of tests, but if the tests are well designed, I rarely feel that as painful as it was when I felt I was battling with the type system. PS: my main experience with static typing was with c++, it's possible that more modern type systems could have improved the situation.