Massive plasma and laser cannons
It's called an Orkulus.
in-gravity-well Novalith cannons
So... basically a stronger version of the Ogrov with more range/firepower? That's not more variety, that's just two units with identical roles.
a massive anti-matter blaster which would vaporize not only chunks of the starbase's healthpoints away but also anything in between it and the starbase.
The Radiance already has an ability called "cleansing brilliance" that does something similar to this, firing a beam that damages its target and anything caught in-between. Its damage is respectable, but nowhere near the power you are implying.
You're suggesting something that is far beyond the level of an "ultimate" capital ship ability, meaning this would be superweapon level in power. At the end of the day, that's already too similar to the Kostura, which damages and stuns everything in the gravity well (extra damage/stun to structures/starbases).
While I'm not opposed to new ideas and content, these are really just suggestions for superpowered versions of stuff that already exists. Uncapped area of effect abilities in particular are extremely rare in this game and usually reserved for elite capital ships; it would totally inappropriate for a cruiser to have an ability that could vapourize entire fleets (and if something to that effect was introduced as a late-game weapon for all factions, it would be silly for it to also be a strong anti-starbase weapon).