Major Partagaz sucks?

With the end of the new Marquee event, we get the one where you no longer earn character shards and instead battle for points. 

im currently on tier 4, which at the low end says level 45 should work. And yet I can’t do enough damage to kill a single unit, dispite having both of the new ISB units at level 50 and 5*. Why is it so difficult? Even if I manage to kill anyone, and usually it’s the tank, they just revive. I don’t usually get frustrated, but every single strategy I’ve tried has failed miserably