On the one hand, I like the ideas that come up. On the other, I see at least three or four distinct ships here.
1. The Dreadnought: An Artillery-like ship with high base damage, a low rate of fire, and long range.
IMO, it should be very slow, given a multi-shot attack, and a minimal attack range. Basically a deployable general purpose artillery battery, something that you slowly tug into a system to have long-range fire support. Maybe it ought to deal damage inversely proportional to a target's armour rating, max HP or somesuch; so as to maintain its capital-killing role.
2. The Splash Damage Ship: A starship with AoE damage. Simple as that, really.
Could also be artillery-like with long range and slow refire rate, which would make it feel very much like real-world artillery...which would be very cool, but I don't think that's necessary. Having something big and splashy is unique enough.
3. The Siege Starship: A Ship capable of dealing damage to and, at the same time, through FFs.
The mechanics themselves are unique enough; all it needs is balancing.
Forgot about the fourth idea. But you get the picture, I do think.