It could work if you used the different classes as the different units in AW. Like use Mercs/Samurai as Infantry, Cavaliers as Tanks, Mages as Artillery, Archers as Anti-Air/Artillery Guns, Pegasus Knights as Helicopters, Wyvern Knights as
Bombers, Kinshi Knights as Fighter Jets, Pirates/Corsairs for navel units, etc.
Does anybody remember Suikoden and the
Army Battle sections? You had to do a rather Rock/Paper/Scissors-like gameplay mixed with Tactic/Army elements where Infantry beat Archers, Archers beat Mages and Mages beat Infantry, that sorta deal.
This was even more evident in Suikoden 2, which did armies in a top-down style like Advance Wars/Fire Emblem. You moved them much like FE/AW, did the Rock/Paper/Scissors-styled battling and some commanders even gave special abilities to their armies, like adding horses and becoming cavalry, Fire spears that dealt damage to multiple enemies, especially to cavalry, Runes for magic effects, etc. Here's some gameplay:
Anyway, I think a FE X AW-styled game or a fantasy-styled Advance Wars has potential and can work.