These missions need to be dialed back on the enemy spawns.  While you have to destroy Warp Gates, you have indestructible teleport beacons that spawn hordes of enemies like every 30 seconds.  Even playing on a powerlevel 1 mission and 30 minutes into it, I could not progress past the first large room because by the time you cleared it out and move up, they would respawn.  Either bump up the respawn time to 2 minutes or make the teleporters breakable.