The primary role of the Evangelist is, as you guesed, to provide frontline fire support and a fighter launching platform. Each such vessel carries a complement of 12 fighters and their support crews. The Avalonian on the other hand, is not a dropship and is actually a heavy cruiser, more massive than the Evangelist and carrying far more guns and fighters.
The Andropov mirrors the Evangelist as a frontline carrier but is somewhat smaller and less heavily armed, its speed makes it a well rounded ship. The Kiev is all about firepower, each can carry up to 6 squadrons (not a pretty sight when they deploy, not if you're on the opposite side). In addition, Kievs have the heaviest weaponry in the mod and quite a bit of armor for defense.