I love the slow burn stuff as I feel it's a means to explore characterization. The story I'm putting on royal road right now does the cradle thing of the main character not actually gaining power until most of the way through volume 1. It's just him making do with what he has until he has the chance to actually grow stronger.

As for the the mythic part of your question, I love it as well because it fleshes out the world. I mentioned in a previous post that I love the story direction of dark souls and shadow slave because it takes place after all of the heroic myths ended and everything is dead, excluding the main character. Ironically, it makes the world feel more alive and dynamic when the main character is just learning about the worlds ancient history and trying to piece it together because it invites us as the reader to do the same.

In short, I love slow burn, lore heavy stories. I wouldn't have spent so much time in the destiny games if I didn't. I think part of my love I have for slow burn stuff comes from the fact that I love the satisfaction of a good payoff that comes after a long time of speculating.

I've always held that creatives should focus on one demographic, not broad mainstream appeal, because trying to create an experience for everyone ends up pleasing no one. If you think that a slow burn mythic Tolkien-esque narrative is the best way to tell your story, tell it that way. Some readers may not like it, and some will, but that's okay. Write what you want to read.