First off, using all your heavy and your super is a mistake. As you damage the boss, that will trigger the Vex to spawn in. Do a little damage, then kill the Vex. Once they're dead, then do more damage to the boss. If you just keep damaging it, you'll cause more and more Vex to appear, until you're overwhelmed. As for hiding places, they do exist. From where you first come up to the boss area, there will be Vex portals to your left and right, and the boss will be on the left side of the area. Stay against the outside wall as much as possible so enemies can't get behind you. Get beside the portal on your left and crouch. You can use the portal to block the boss from shooting you, and kill the Vex as they come out of the portal. When you've done enough damage to the boss, it will rotate around behind you to the right side of the area. When it moves, stay crouched, and move along the wall to the portal to the right, and it won't be able to shoot you while it moves. Also, the large Minotaurs that are shielded can also be used as cover. The boss can't shoot through their shields, so until they start moving, you can take cover behind them, just make sure you don't step backwards too far, or you'll fall off the platform.
Just go back to orbit and search another strike. I don’t play that strike because one, I’m sick of infinite forest and two, dendron the root Mind is a pain boss.