The "Badly Burning" debuff does 30% MaxHp damage, regardless of your defense or resistance values. The fire resistance only helps against fire element attacks/spells, not against debuffs.
The targeting of the enemies is randomized. You increase the chance for them to attack your tank by using his abilities, but it's never a 100% chance for them to attack him.
Luck affects only the chance of getting affected by negative status effects. It doesn't change your aggro chance, drops, or evasion/crit chance.