The game doesn't have tanks, so trying to tank is akin to using a chocolate teapot.
I can't say I'm finding Madora ignored like you find, the enemies I face go for the closest party member usually so either you're just unlucky, or you need to position your people in a different manner. Maybe you need to plant environmental debris in a better pattern because I can only assume you leave a straight path to your casters.
As for my priority target, I'm finding the enemy archers are more deadly than the mages after Cyseal. They often get to fire two CC arrows on the initial turn
