Despite how it sounds, this achievement can be easy.
I completed it via selecting a [ROBOT ENEMY] Mission, look for the objective "Thin the enemy lines." (Where you have to kill a certain amount of enemies.) unlike the insects you don't get overwhelmed so easily and in the early rounds you can destroy everything in the drop-shop with Grenade Launchers or other AOE weapons.
Use turrets, orbital bombardments and other AOE offensive abilities if required.
I managed to do this as a Duo, the only dangers we found are Tanks and if you're unlucky a Hulk. Play safe and take out the enemies as they fall out the drop-ships and it'll be relatively easy.