I just completed this Saturday and it was hell. After trying multiple suits, it was the Shining Gundam that did it for me, if you can believe it.
Anyway, the method I did was a very brute force one, but I was able to beat it by killing Gun-EZs that were far enough to not be covered by their teammates and/or priortizing and killing one as quickly as I could while dogding enemy fire as best as I could. I also picked off the weaker ones my teammate was able to do good damage on whenever the opprotunity arose. When the V-Gundam Hexa and another Gun-EZ comes after the second wave, I focused on the Gun-EZ so that they couldn't provide cover assist or cover fire to Hexa, making it easier to deal with Hexa. I also used burst here to kill the Gun-EZ as quickly as possible and any other enemy units if I had gauge left.
I did all of this without any customations, so I would use some that'll increase damage, mobility, ability cooldown, etc if you want to make this easier and if you have them. You can still get a S-Rank on this mission if your teammates dies only once.