True. But I was pushing back against the opposite, that D&D doesn't have the printing press and thus shouldn't have high literacy. It does have the printing press, and can (but does not necessarily need to) have high literacy. You can choose either way, but don't blame it on missing the printing press.
And as far as old school == based on medieval europe...D&D has been anachronistic since day 1. It's had alien spaceships, out-of-period weapons and armor, "feudal" (but not in the real sense) governments, high literacy, inappropriate technology, etc since the very beginning. It's never been based on medieval europe. And we're in the 5e forum, which is even less based on medieval europe than any edition (except maybe 4e). 5e is based on D&D, mostly. With circular influence from popular media (most of which was influenced by earlier editions of D&D). It's not realistic. It's not designed to be realistic. It's an entirely different fictional world with entirely different history.