> Most of the data I deal with are strings with their own validation and formatting rules that are complicated and at the same time usually need to be permissive

this is exactly where a good type system helps: you have an unvalidated string and a validated string which you make incompatible at the type level, thus eliminating a whole class of possible mistakes. same with object ids, etc.

don't need haskell for this, either: https://brightinventions.pl/blog/branding-flavoring/