not entirely
you can definitely argue that the universe although fictional is clearly based on our history to some extent
the technology is very similar to the technology of our medieval times
there's swords, shields castles etc.
they even have a lot of the mythical creatures that started popping up around that time(a time when a lot of people actually believed these myths)
trolls, giants dragons witches etc.
in that regard more medieval sounding voice acting would certainly add to the believability of the whole universe, at leas to some people
that being said, personally I'm not that bothered by it.
I would definitely prefer more "accurate" voice acting to match the rest of the world
but I also have to admit that due to dozens of years of pop culture, movies games books etc, I've kind of gotten use to it.