What is your experience with refactoring, especially a big project? This is where static typing helps a lot ihmo. Especially if you are in a startup like environment where things tend to change quickly.
I actually did pursue static typing (w/ type annotations and Dialyzer) at one point, but quickly lost interest, since it didn't really seem to add much. Having comprehensive tests, on the other hand, was crucial - especially since I could use pattern matching within those tests to make assertions about expected inputs and outputs.
I will say that there were bugs that compile-time type checking probably would've caught, but tests also readily caught them. The same can likely be said for current bugs. It's ultimately the same idea: validate that your code adheres to the expected API and behavior; only difference is that the validation happens in different places.