I played the Onjective Challenge and tore my hair out at how loving useless my team was.
I suggest getting the Light body type, and sprint loving everywhere. Usually once the enemy gets there, they camp and it's literally impossible to clear it out. Move as fast as you can, and try to climb / wall jump in hidden areas. Not to mention the time limit. Another tip is, as soon as you grab the Intel, sprint like hell to upload it, because if you die, they reset it.
I highly suggest completing all the other challenges first, because you get more gear.