I’ve noticed this is one of the battles people struggle with the most, and I think I have the solution. Most of the time, everyone has vehicles left over from round 4 when you face the grunt mech. You get annihilated because there are a million Knights who have River of Light. Vehicles are extremely ineffective on this encounter because you can’t dodge their shots, and you waste your reqs trying to use vehicles. You need to call in ranged weapon reqs instead. Keep damaging the grunt until you blast it’s nose off. Once the nose is off, use snipers to hit the nose, the “critical hit” area. Last night, I killed the grunt mech with 2/5 of its total health in a SINGLE shot from the legendary H2 Beam Rifle. We then had 3 mins to call the 2 mythic hunters that spawn, which was then a piece of cake. Good luck everyone and I hope this helps!