Wow, I was about to make the EXACT same thread, but...
My renown was 100. I'm piloting Zero Savins with 3 other pilots. Even before I can _turn_ to face the opponent, I lose the mission. I mean, at that renown, there are Krakens throwing nukes, and the mission starts with them _already_ in range of the ship being escorted (~100 m). The cruiser was rubble even before I get a shot out.
Anyway, I went back to the space station... then found the space station selling nucleonic rocs, which features +3 acc ARMORIGNORE SWARM missiles. I ripped out all the other weaponry from the savins and gave my entire lance 2 of these missiles, raised my renown to 100 and went into another escort mission.
The missiles helped a lot. Even if I weren't facing the opponents initially, my lancemates could fire these missiles and take out 2 or 3 mecha per shot.
Unfortunately, I now have a rearming bill of 300k.
Without said missiles on multiple mechs in a lance (to help guarantee that at least one of your lancemates is facing in the right direction when the mission starts), I'm not sure the mission is consistently winnable at higher renown. Opponents start within range, lob a nuke or swarm missile, bam mission over even before I get to shoot.
So it sounds like, if I had the patience to bring my renown up afterward, I could get by by lowering my renown down to zero; surely the cruiser can survive a couple of shots from a buru buru peashooter?
My renown was more like 60, so none of the attackers was quite so scary, but a whole lot of weak attackers still means a lot of shots fired at the cruiser, and I'm also not so heavily prepared as you were.
It seems to me that you could make the mission fairer by moving the different parties. If the mission is "defend the cruiser" the player would naturally start between the cruiser and the attackers. If it's "you come upon some mecha attacking a cruiser", then this doesn't make so much sense, but the attackers could be between the cruiser and the player (so that if they turn to face the player they have to stop shooting at the cruiser) or at three different corners. In any case it seems to me the map should be big enough that all three parties are initially well out of range of each other.
Another approach would be making the cruiser tougher; if it could stand up to more rounds of attacks, that would give the player more time to do something. It'd have to be scaled to the player's renown, since a cruiser that could hold out against renown-100 enemies is in no danger from a swarm of renown-50 enemies. You'd also give it more armor and DP but not good weapons, since you don't want it to do any significant defeating of enemies (though there's something to be said, flavour-wise, for one weapon that did massive damage but was very slow; DC80X10 but fires only once every five rounds, maybe). I'm not sure this can really work, though, since it's a bit crazy to give the cruiser a "dodge" roll, and many GH attacks do overwhelming amounts of damage if they actually hit. But it does have some appeal from a flavour point of view - the cruiser is taking hits while you race to its rescue! I think I'd prefer to combine this with the above, so that the user pops up behind the attackers as they blast away at the cruiser and races in to its rescue; any attackers that turn to defend themselves are taking heat off the cruiser.
It's also possible that there's nothing wrong here - if this is a major "boss battle" in the main story, well, it should probably be difficult. But I think currently it feels "unfair" rather than simply difficult; it seems as if the only way to beat it is to use specific, strange, tactics that don't make much sense in any other context (e.g. lower your renown, have an extremely-high-damage extremely-long-range SWARM weapon on all your lancemates).
