Is that a tutorial video or a mister bean parody? It can be done easy with 3 guys (shit gear, no statted or HPA).
I love your formation, straight line with every guy sticked to the next one for maximum minigun splash damage and an unarmed tank tanking for the enemy. Keep an eye on your log mantis, if 2 hits are displayed with a straight bursting weapon, you are doing something wrong. It can happen once or twice in a row, but you shot your friend so hard he had to ask you to stop lol. Put 3 tanky guys in a line, or tough critbursters with EPM loaded pancors, one hex space between each guy and shoot. If you have aimers/rocketeers put them in a second line at least 3 or 4 hexes behind if you really want to swarm that poor miniboss. I'm pretty sure you can even do it with a hexer and a HTH KD, like in ares, but I never tested.