You forgot one thing....

In the initial EF/Minbari encounter, the Minbari had been surprised. Every single ship in the fleet had concentrated their fire on Dukhat's ship. In our situation though, both sides are expecting conflict. The Omegas and the fighter's themselves would be harassed by the fighter complement of the warcruiser.
Also, the Warcruisers front guns can dub as her side guns. And her two flanking fin guns can also dub as rear guns too. Remember in Sky Full of Stars, we actually see beams coming out of the tips of the fins. Not the barrel end, but the rear " sharp" end. There is also misconception that the eight smaller guns below the big double pronged gun are only anti-fighter guns. This is untrue. In Shadow Dancing, a Shadow cruiser was stopped dead in its tracks by one of those guns. As for that Nova being able to ram the warcruiser, notice that the cruiser was already damaged. What happened that led up to that scene? All we know is that the Nova was able to ram a already damaged cruiser.