You definitely need cover though. Your team members are rubbish so you're essentially on your own against everyone else.
Btw, that strategy doesn't always work. Sometimes the AI gets confused and remains at its spawnpoint, so you need to pick them off one-by-one with a sniper rifle if you have line of sight or move closer if you don't. Note that moving closer can fail the mission if you go to far because you'll be out of the designated war area.