I feel like you're out of line here Micah, because no TSR or WotC D&D setting has attempted to do anything except "history as a pretty backdrop", with the posssssssssssssible of Taladas (or to a lesser extent Planescape - no accident both were Zeb Cook, I suspect), in either the 20th or 21st century. Oh and Eberron - Eberron did seriously think it through - that's our one real exception. But that doesn't have a medieval mindset, it has a sort of "turn of the century" (no, the other turn of the century < weeps in old >) one.
The whole "modern perspective" thing could 100% be argued about 1970s Greyhawk, or 1980s Forgotten Realms. Elements of Greyhawk were profoundly coloured by 20th century American takes on Christianity (which obviously can't be discussed in detail here, I'm aware), and there was absolutely no serious, Warhammer-esque attempt to get into the mindsets of a different people. You just got a kind of joke-y/meme-y collection of "kewl godz". With the FR you got, and I hope it's okay to say this, kind of "Gods Ed Greenwood wouldn't kick out of a swinging sex party". Again the FR didn't, in the 1980s, or 1990s, make a serious attempt to "get into a different mindset", it was just piles of assumptions, some contradictory assumptions, all on top of each other. As noted, a lot of what 1990s TSR writers assumed about the FR kind of hard-contradicted what Greenwood seemed to be assuming, and neither was truly thought-through or considered.
Now I mention Warhammer for a reason, because that's helps show how no official D&D setting - except Eberron - has ever "tried to get into a different mindset". To get into a different mindset you need to actually put the work in, actually think stuff through, have consistent cosmologies. Throw out stuff that doesn't fit before it even reaches the published page. And TSR and WotC just haven't really done that. Could they? Absolutely. There's no lack of talent. Eberron did it, Taladas sort of did, but those both did it because they were the singular visions of specific authors with strong philosophical ideas and strong conceptualization, and frankly, open minds, not people who were a bit flip about it, nor who had narrow visions of what religion "could be" (as I would assert the people who wrote a lot of 2E's FR religion books did).