make a smaller limit, then. buildings are weaker than bunkers; use AT-STs; they're cheap and plex troopers aren't entirely deadly against them.
In a bunker, i am pretty sure that 2-3 squads of plex can take down 8-12 atst's easily. Even with the ATST's using thier ability. In a building, like a factory, which has only slighlty less health....well its still kinda ridiculous....
attacking a fortified position without armor support and air support is supposed to get your force slaughtered; attackers almost always suffer heavier casualties than defenders.
Vs. A bunker with 5 plex
Armor support = AT-AT (which is supposed to be the most uber land unit)= Will be destroyed
Armor support = 2-M ---> Pwn by Plex
Air Support = Lancet----->" "
Air Support = Bombing Run --> Effective, easily pwned by 1 anti air turret, 2 runs needed
That leaves only Orbital bombardment and Artillery as effective counters.....which means if you are at low tech, then you will have HUGE casualties against rebels, since you dont have SPMATS or large fleets for effective bombardment.
And IF the imperials ever get rocket troopers....welll the rebels will only have artillery because thier bombardment is retardedly useless