I don't think they made any glaring errors so far. You could say keeping their mages back and stuff is questionable, but tbh, they've got so many chod soldiers that wearing the enemy down with the less valuable troops isn't a bad idea. I've definitely seen worse examples of villains being bad generals before (though I interpret that as them being bad at leading troops in battle, when you could be referring to them being bad at leading in general).
The biggest problem is the landscape, it favors the good guys. The narrow canyons mean only a few of the attackers can enter. That means their numbers mean nothing. Worse the heroes are open to reinforcements and supplies. But the heroes are just as bad. They should have had archers combat medics mages in the back, swordsmen in the middle, and pikemen in front to stop a charge.