Ya I tried it a few times without ordering my fireteam to target one, just shoot what ever and that wasn't working. So I switched to basically tanking the wardens and have them target one while its chasing me. I was pretty satisfying when my ground pound did the final blow though. And those damn turrets holy **** they were annoying. Even after killing the ones on the side I was at, the ones across the map would still find a way to target me half the time. A little tip I learned though, you can use the warden to shield yourself from the turrets. Dunno if they damage him though.This was probably the most frustrating thing ever in a video game for myself.
I took them out by ordering my fireteam to target and when distracted got shots in with the weapons. Also took out a few of the laser turrets before killing the last warden.