Yes, people spoke casually in ye olden days too
Another Linguistic Pondering for you: in book/TV/film reviews for stories set in historical (or prehistoric) times, people often complain if the dialogue is casual, because that feels "too modern." The fallacy there is the notion that everyone was always formal in ye olden days. Which they were not! Humans have always been humans. All languages have always had a casual register and options of informal usage.
The issue on what would make it "feel too modern" is more one of translation: e.g., if you decide "'sup, dude," is the appropriate casual translation for a friend's greeting in ancient Rome, then yeah, that will seem anachronistic, even though technically having them speak English at all is inaccurate, so the whole thing is in translation. Even so, what can we substitute? We know, if we think about it for five seconds, that close friends likely didn't greet each other with "Good afternoon, my friend," but rather with something along the lines of "'sup, dude." But what can we use? "Hey"? "Hi there"? "How's it going"? Nope, all those will get you flagged "too modern" too, unfair though that is. We have to fall back on "Good afternoon, my friend" or else it doesn't sound "historical." Which is stupid, now, isn't it?
Part of the issue, I suppose, is that casual wording, being akin to slang, falls out of usage fairly quickly, so even what was technically casual in, for instance, Shakespeare's time now sounds archaic and therefore "formal" to our ears--because of the above fallacy that anything archaic must be formal. (Did you know that "thou" was the informal 2nd person term of address, and "you" was the formal? Yet try using "thou" today without sounding super-formal.)
In short, I wish more of the world freely accepted that people have always had a casual register (alongside a formal register), throughout all of time, and therefore using casual English as the equivalent is not an error, but rather an accurate translation.