Nope, not the attacker's arcs.

I actually 2 shot an ISD with an MC80 assault cruiser with Ackbar, Defiance and XI7 that my opponent unwisely gave me advanced gunnery on. I had damage left over too. I think the lesson here is that large ships are large and tanky, but can easily die from full health in a single turn. Gone are the core set days where it felt like the rebels had to throw everything at they had at a VSD to hopefully kill it on turn 6.

I wouldn't say easily, but yes very possible if a player is careless as is evident from all the topics about it happening Which is good I think. Most if not all of the cases of ISD's getting destroyed in a single turn can be fairly easily prevented though, its mostly just that the ISD is so imposing and the Rebel ships are so much smaller, people overestimate the ISD and underestimate the Rebel firepower. Ackbar admittedly is rather powerful, but becomes less so when the Rebels need to close in with the Imperials rather than the Imperials making a beeline towards the Rebels which is something you see happening quite often ("If I move my ISD directly towards the Rebel line, it'll be subjected to the broadside firepower of the entire rebel fleet....oh what the heck, it can take it! Charge!" *Boom*). I expect when new tactics evolve Ackbar becomes less of a 'must take'.