Solutions to any given problem are necessarily described with types. You can check those types at runtime or you can check them at compile time, but meaningful programs are typed. If you've got a function that takes a string and your type system lets you run a program where you pass an int to it... did it just allow you to 'quickly iterate'? Sure, you're running a program sooner, but you're going to run into the same type error (function expects string, not int).

Maybe in a larger code base you could argue that the effort involved in satisfying typechecks meaningfully slows down iteration, but even then it's clear that being able to compute the list of type errors you introduced elsewhere (via static typing semantics/analysis) is valuable.