You have to kill the gun on the troop ship in the final boss room or you get nuked from above. There are two types of ships snow in the Arms Dealer. One has a gun upfront that will make your life miserable if you don't kill the gun. It's the one that drops cabal, not the one that just flies around. Also, the final boss room spawns six turrets as soon as you come up from the platform, and you need to take them out fast. There is cover on the platform. The turrets respawn just below where the chest spawns at the end after the boss goes immune and up to his shielded tower. Many of the strikes have been changed. Returning players might benefit from watching a recent video of the strike they are doing if they are struggling. Hope that helps a bit.