[mafribe]

Most programming languages with Damas-Hindley-Milner do not prevent you from using explicit type annotation, and inventing semantically meaningful type names.

More importantly, I think the reason why error messages are sparse and not meaningful in languages with Damas-Hindley-Milner is that nobody bothered to improve the situation. And the reason why nobody botheres is that it's simply not a problem in practise. Any even moderately experienced programmer can easily detect and fix typing errors as they are given in Haskell, Ocaml, F#, Scala etc.