The Imperial attack actually started rather badly. Admittedly they did not know about Vasilik's special power- though there's a lesson about the unknown in warfare- but they were already not engaging on the East, so the East obviously could not be broken through, the area where Vasilik was could not be broken through, and the Imperials simply declinesdto attack North which meant there was only one possible avenue for advance, and even that would depend on dice rolling. With two sectors the Rebels did nort have to defend, they could have made good their losses for some time, and if the Imperials broke through in one sector alone they would simply find themselves surrounded.
Aware that my broad knowledge of all sides of the battle gave me more insight into things than you as players did, I hinted heavily to the Imperials that this was an issue, because I felt it was unlikely that the battle would go on without anyone noticing the problem. Mind you, stupider things have been tried over and over again in wartime.
The Imperials got a first turn breach, but other than that it did at first look as if the Rebels might have a better time of it.
The Imperials were somewhat undermanned due to Rebel activity in the Jungle, but Imperial work in stopping weapons reduced defensive units too. Most critically, the Rebels failed to stop any of the AT-AT units getting in (in contrast to the off-line game, where only two units got to the final battle), meaning that the Imperials had a very lesiurely time about picking their assaults. The Rebels did not try to enter the camp themselves to sabotage the AT-ATs, and it was made more difficult for them right from the very first week of the game when they ordered in their weapons; that could have been done better. Rebel failure to destroy the artillery was also a shame, especially because it certainly could have been done- certainly the second unit, maybe the third, and definitely the third if they had not lost some of their air power earlier in the story.
After that, things went generally evens but the Rebels became too obsessed with holding ground they simply could not hold, and threw away their units. These units could instead have held in the East and either reinforced other areas under attack or even been used to attack Imperials inside the city.
The Rebels could never have succeed- literally speaking they could never have succeeded at all; Lanzar would fall eventually even if the Imperials had to bring half the fleet in. But in the terms of the story the Rebels could not have succeeded either because they failed to delay the battle on the political side, and I believe the Imperials had a full day left before their deadline was up. The best the Rebels could hope for was to make the battle take so long as to humiliate the Imperials; they were a fgew hours short of that. Nonetheless, the battle was not won impressively fast either. Tne Emperor is satisified, but he's hardly overjoyed.