I'm going back to Exalted again now that I've got a few more games under my belt. It's maybe a bit more complex then is needed here, but there's a huge amount that can be trimmed. Movement is never "okay, your turn, you can move and take an action". You can always move, even while other things are happening. Permanent Essence rating can be the "strength" of a *-mancer, while the Charm trees are cut back to one per metal per discipline (Allomancy: Ironpushing, Feruchemy: Steelstuff) and I imagine that the trees won't be very long. Abilities representing knowledge of *-mancy are needed, though there could also be ones for a particular metal. Mass combat is great and all, but is done such that the skills of commanders are merely enhanced by their troops. Hard to explain, but the book describes armies as being "worn" by commanders. Mechanically it works out. The whole system has enough situational modifiers to be quite gritty, but you can junk those and keep right on going. It's granular enough to handle gritty, yet doesn't suffer if you take much of the gritty out for a more cinematic feel.
I say Exalted only because I don't feel d20 is a good choice and Exalted is the only other RPG I'm currently playing. I will try to get a hold of Feng Shui, a current draft of FATE Generic, and any other system I can think of. It's too rich of a world not to try to wrap a RPG around.