In the age of unicode (and modern computing in general), all of this is more headache than it's worth. What is actually important is that you limit the size of an HTTP request to your server (perhaps making some exceptions for file upload endpoints). As long as the user's form entries fit within that, let them do what they want.
I don't it's practical or useful to just say "limit the size of entire requests" and just ignore all the real world reasons you'd want to actually validate/check data before putting it in your database. The logic you're using is how we have bugs and security holes. This persons write-up gives specific and detailed information that's genuinely useful.
If you can get away with that, that's great. But I feel like there are still plenty of cases where you want to limit the lengths of particular fields (and communicate to the user which lengths were exceeded).
