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Sounds like The Coconut Effect to me. Medieval folk probably wouldn't be mentioning faith all the time because it would taken as granted, unless there was a reason to (church officials in the area, accusations of witchcraft, plagues, etc.)
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Hmmm, I guess that could be it. I have also seen this from the other side, like Christopher Stasheff's Wizard in Rhyme books. He set out to make a fantasy series in which God and religion are as integral and important as magic and everything else, because he had never seen any series where that was done, and he felt this made no sense because to the medieval mindset Christianity was infallible and the people saw matters of God and faith in everything.
So there are people who want to make something more prevalent because they feel it should be there for accuracy and has been left out, and other people who downplay its presence.
What's the trope for where a medium is set in a time or place where a certain thing should appear, or at least be very prevalent...but it isn't? It's not Did Not Do The Research, because the thing in question does appear, it's just nowhere near as emphasized as it should be (or as we expect it to be).
The example I am particularly thinking of is a work set in medieval times where you expect Christianity and religion to be mentioned a lot, but instead it's just...sort of in the background, like local flavor.