Whoot! I just finished that mission with Xinny/Zero on insane. CHRIST AND ALLAH that was hard. Honestly, -that- is the hardest part of the game for me. I'm not sure why so many people complain that Darkest Hour and Delenda Est are hard, they have just the right balance. But this one... I don't know how you guys ever got through that fight enough times to properly beta test the mission :-p
It's SO much better if you draw them out and hit them one at a time, but even then everything has to go perfectly because the wingmen are just seconds from being on top of you. One trebuchet and it's goodnight, one 2 second burst of gunfire and you're dead. I actually made it through once before only to get killed by the second wing before Beta arrives. Lamely enough I died that time because Beta 3 crashed into me and knocked out the 15% hull I had left. I actually managed to evade ALL the gunfire and missiles (or at least keep my shields from dying on me) only to have my wingmate crash into me. LAME!
Anyway, I got through it a little while ago. You know what would be really great after you defeat the first group of fighters? A checkpoint

. Don't change the difficulty of the mission though! Fighting those guys SHOULDN'T be easy, it's fine as is. Sure it's INSANELY hard but it's not like you have to beat it in order to advance the campaign.
Quutamo was such a good choice though.