They are in no way comparable in scope. Introducing a type system gradually doesn't break any compatibility, within the module or outside the module. It doesn't

They are in no way comparable in scope. Introducing a type system gradually doesn't break any compatibility, within the module or outside the module. It doesn't require you to understand what the legacy code is doing. Rewriting in a different language also means different libraries, different glue code, different interfaces, different everything.