Pretty simple strategy here. You need to fight a war of attrition with the Zuma since they cannot maintain their CS once they're engaged in earnest. Sure, if they blow up your army you have to go refit, but you'll leave a nice dent in theirs too. Then next time you fight them they're not as strong. And then the third time you blow them apart. They don't have a capital a couple days' travel away, and their leader is probably just as killable as a hero assuming Fang Fang functions in the same vein as Nightfall/Midnight/Darkest Hour/Overlord/Every other Daimon leader in the game.
It's not unwinnable by any stretch of the imagination, you just refuse to even try. Using OOC complaining to beat them looks pretty sad.
