Yeah, the evidence here is mostly anecdotal but, while we’re trading anecdotes, I think you have to distinguish Smalltalk/Clojure/Common Lisp from other dynamic languages. Most dynamic language essentially work like statically-typed languages without typechecking: you put code in a file and then run it all at once (or run unit tests) and see what happens. The languages I mention actually bring your development environment to runtime (twisted manhole and pry are the closest things I can think of here) so, you don’t have to run the whole thing, you can just run the parts you care about and see what they do.

That being said, my experience isn’t the same: I’ve been able to make helpful changes to dynamically-typed codebases in roughly the same amount of time as to static codebases. I’ve never really identified what it is about how I approach code that makes a difference here, but I think it is because I think about changes in terms of operational equivalence (e.g. l.map(a).map(b) === l.map(compose(b, a)) ) rather than in terms of data types.