This is a great example of the difference between theory and practice. In theory, you're correct and type errors could be hiding out in a dynamically-typed cod

This is a great example of the difference between theory and practice. In theory, you're correct and type errors could be hiding out in a dynamically-typed codebase after a language version upgrade, lying in wait to take your system down. In practice, nothing like what you're describing has ever happened to me when working in large (1M+ LOC) Ruby and Python codebases. In my experience the difference maker is testing, not type checking. I've worked in poorly tested Java codebases where upgrading a dependency still allowed the application to compile and deploy successfully, but then at runtime things started blowing up randomly. Meanwhile with well-tested dynamically-typed code I've never had any such issues.