If you want big Battle of Endorish missions that aren't crap you've gotta break up the battle.
Make the player zip between sectors and perform different actions in each of them - replace Epsilon in Sector 3, hold out for 4 minutes - regroup to Sector 5, launch an offensive with Beta into Sector 1 ect. ect.
Simulate the rest of the battle that's far from the player - there don't have to be that many ships. Just make sure some booms and big ships can be seen.
A work heavy but good solution is creating a skybox with an image of the rest of the battle added.
A good Big Battle isn't about the scale, or lots of things kicking each other's teeth - it's the tactics, the sense of being a working part of a big battle group instead a trigger frenzy.
I've never seen that done before, therefore I still hold my opinion that it is possible to do a good big mission, but it's not about adding tons of stuff.