Quite a shame we never saw the Destiny Ascension fire a shot during that cinematic. It just kinda sat around and looked cool until it started taking fire, at which point it just became sad. I was kind of hoping for a scene where it faced down a swarm of Geth ships, killing many but eventually being overwhelmed by force of numbers, or maybe a scene where it got into a one on one slugfest with Sovereign, but in the end it just kind of sat there.
Honestly though, I think that it never fired a shot onscreen because Bioware wasn't sure where to put the main gun. I mean, spinal cannons become more powerful as their length increases, to the point where Dreadnought cannons fire with the power of a nuclear weapon, and the Destiny Ascension is only about as long as a regular dreadnought. It would have made more sense to mount the spinal gun vertically, but then that weird hoop thing would have gotten in the way of a massive two kilometer long oneshot gun. All in all, Asari ships in general seem rather poorly thought out, with large frontal cross-sections, short designs that inhibit spinal gun positioning, and those weird hoop engine things that seem like a horrible waste of space when compared to a regular engine, but then again, it's a game so form takes precedence over function. Still, poking holes in sci-fi ships like this is something of a pastime for me, so I tend to do it regardless, and the Asari give me plenty of designs to pick on! Stupid, stupid Asari.