I'm afraid the Rebels and Rieekan just lacked the firepower, though Blizzard Force lacks anything to effectively counter Rieekan's air forces, their units are so heavily armored and so strong they will with time punch through the Rebel's defensive lines and annihilate opfor command
There will of course be imperial casualties, especially because of said lack of anti air weaponry, but as soon as the rebel staging area is threatened, there's nothing more they can do
Well don't forget, the Wilderness Fighters have heavy weapons with them here for this scenario. Which means...
So they have the firepower along with any other heavy weaponry that I am forgetting, to cause significant damage.