Why do you imagine types slow velocity? My experience is the opposite. I occasionally prototype in Go and then backport to Python (to integrate with our application) because I can iterate so much more quickly (yes, Python has type annotations, but the ergonomics are poor and the type checker is immature).
Experience. Again, not talking about a mature project, but a new one in the design phase. Types (like unit tests) are extra work at this point until a good design is discovered. Which takes time to think about.
