Perhaps it's my age but I don't find Roman numerals noticeably slower to read than Arabic for the usual use case of recent centuries.

Yeah, but XVIII has a certain appeal to it that your way just can’t match.

> is faster for the writer

For the whole letter?

> reader

Only if the reader completely unfamiliar with Roman numbering system. I didn't even thought about it until I saw your comment. Get off my lawn, son?

I'm guessing it played well with the WWII lettering.

Using Roman numerals for centuries is conventional in Romance languages.