The platforms are definitely the most dangerous spot in the fight. Everything in the arena can kill you very fast. Ads, ogres, drive by shooting from the tomb ship, running back and forth to detonate bombs, gotta worry about knights, the platforms are tough.
Relic runner usually isn't too bad unless you always start from the right side, because after grabbing the spark you have to run up from the back of the room to up front to get the vessel. After that, you're golden.
The middle guys normally just stay in a titan bubble and kill stuff for the duration of the encounter, except for the last detonation when one of those guys needs to go get a bomb. And really at that point, it's not the end of the world if someone dies and all damage registered on Oryx like it should.