yea same, at the start im able to take out 2 axe throwers and the 2 rocket guys before the mage comes in. everything seems fine jump across while in the air, avengers shield the last to axe guys, slap lights hammer on them and zerg the mage by the time im done the axe guys get one last shield and there dead, but when i check the ship its has half hp or less even though four of the six adds on the horde ship are dead.
With the reavers i have them attacking the ally boss not the ship, could this be the problem? does the damage he gets affect the ship as well?
You probably forget to kill adds spawning on your gunship. They hit pretty hard.
EDIT: Soloed with my rogue first day the patch was on. It is not easy, but it can be defeated solo.