As has been pointed out, while TEC and Advent recieved new ships dedicated to taking out enemy structures, the Vasari had their anti-structure weapons tacked on to their starbase, which leaves a gap in their assault ability.  Now sure they could just add a Vasari ship for killing bases, but I like keeping the different races unique so I want to provide some alternative suggestions.  These could all be implemented together, or seperately, or cherry pick from among them.

1. The first possibility, and certainly the one that requires the least amount of new assets, is to buff the Vulkoras Desolator's Assault specialization ability, specifically the increase in damage against structures.  This would be easy to do, but keeping it as an upgrade on a cap ship may require some other options to go along with it.
2. The second idea is to give an option to Jarrun Migrators for a rapid starbase construction.  This would cost significantly more than the standard construction, but allow the Orkulus to be built quickly in an enemy area, possibly even automatically upgrading its weapons a level so it come out ready to tear up enemy structures.  In order to make this only attractive for building offensive starbases, perhaps it would permanantly double the upgrade time for all other upgrades to the starbase, or maybe increase the cost of all upgrades, or some combination.
3. The third idea is actually an idea I had a whle ago just for fun.  Certain Vasari ships would gain the ability to construct a new strike craft squadron, which would be an anti-structure cruise missile.  Each squad would only have a single missile, and when undocked they would automatically make a bee line for the nearest structure and detonate, dealing damage as appropriate.  This would require some AI tweaks probably but would be interesting, plus it would also give reason to keep strike craft docked, as you could stock up your missiles and then let a few fly at once.