I get where you're coming from a lot better when you put it in those terms. I think I'm a lot closer to how they thought about religion in the medieval-type mindset than most people here, not necessarily in specific details of practice and theology or in degree of virtue or faith, but the intertwining in all other aspects of life, and seeing everything through a religious prism, but it doesn't really seem like ANY author gets it. In Martin's books, until aFfC with the rise of the Sparrows, I didn't see the point of it being there at all. The state of the faith of the Seven was more like a modern secular society, with people paying lip service as an aspect of their culture (and going to the church/temple/sept for important ceremonies as many secular people do today) than part of the lifestyle.

And of course, for the pre-christian world, religion's place in society was entirely different. From what I've read, the Romans, for instance, and some of the Greek cultures might not have been big on doctrine or sin or theology, but were what we would deem extremely superstitious, constantly attributing all sorts of things to the supernatural, and making propitious gestures, and having that stuff seriously impact their choices and actions. By contrast, most fantasy works seem to regard religion as a discrete aspect of their lives that they never worried about beyond their specific rituals and practices, often with practical purposes.

To me that's like only thinking about sex when you're in bed with a partner, and sex having absolutely no impact or considerations in any other choices or actions you take for all the rest of the day. Sexual attraction and titillation would play no role in anything, there would be no suggestive advertising, clothing would be worn entirely for practical considerations and aesthetic display of the garments, rather than accentuating the attractiveness of the body beneath, and mates or partners would be selected on practical grounds and personal compatibility, with attraction playing no part in process. That's the best comparison I can think of to the way religion is most commonly used in fantasy worlds.

Even in fantasy books with an extensive mythology, the gods are usually just for decoration. When they do play a role, it is as simply another form of antagonistic tyrant or an additional degree of power for various characters (like in Malazan), or to explain a certain rule peculiar to that setting. There are also cases where they are a source of magical power, in that organized clergy call upon them to do magic, but that is certainly unlike any real world religious experiences.

Aside from maybe Warhammer, I can't think of a single fantasy property where the normal everyday people might be inspired to wage a crusade or jihad purely on religious motivation (even allowing for the sort of self-serving impulses that no doubt motivated many real-world holy warriors). They might call it a crusade when they go after their equivalent of Sauron or the Dark One, but that's just a normal fight for freedom dressed up in religious clothes. It's not the same as fighting to retrieve something solely because you think it is important to God or to eradicate something just because you believe it is hateful to Him or to bring a powerful and fundamental truth to people who are unreasonably resisting their own betterment.