Vasari Starbase Counters

fully upgraded Orkulas are monsters. the real issue is going to be the Frontal Shield, which makes it almost completely invulnerable from the front 180 degree attack arc. the shield won't be active 100% of the time but it will still be the single biggest obstacle to actually killing the thing. basically this is the Sins equivalent of a boss fight (if this was an RPG or something like that). you have to take the thing on piece by piece and work it in phases.

the first phase of your assault will be to take out any defending squadrons in the grav well. you'll need to nuke any hangar defenses and bring a dedicated group of your own carriers with fighter squadrons. their only job is to take out the squadrons stationed at the Orkulas itself. 

once the grav well is clear of fighters you're going to need to kill the anti-matter on the Orkulas. if it has AM then you'll never make a dent in it between Frontal Shield and Debris Vortex. but without AM it can't block shots and it can't repair at super-speed.  TEC and Advent have good ways to drain AM but Vasari doesn't. you may have to skip this step and go right to phase 3 of the assault in that case.

the final phase is the direct confrontation. if you've drained its AM then you can just frag it with LRF and anti-structure cruisers, no problem. goes way faster if you've got a focus fire boosting ability like Designate Target, or Shield Degradation, or Nano-Disassembler. if you couldn't drain its AM first then you're going to have to use mostly bomber squadrons to take it out. bombers will attack it from the rear, invalidating its frontal shield. if you carefully micro your ships to stay out of its range you won't create enough Debris for it to self-repair with the Vortex so the damage will actually stick. bombers are a great solution to starbases in general as long as you've cleared the well of fighters first. 

i know that designate target can't target a starbase, at least the stationary ones.

If you are Vasari, try to get that siege capital ship, the one which has siege platforms and assault specialization. Get the assault specization to level 3 on about 4 of them and you have a ship that does better structure damage than a torpedo cruiser and has the HP to stay in the fight for a long time. And if you can, try to hit the planet with a Kosturas cannon, that should even the odds a bit.

Late game as Vasari

I have 1 of each Capital Ship with an extra Kortul Desvastator, Skirantra Carrier and Vulkoras Desolator.

Supporting the Capital Ships I have 20 Revastra Skirmishers and matching Kanrak Assailants and 10-12 Junsurak Sentinel with 10-15 Lasurak Transporter, Stilakus Subverter and Serevun Overseer and 20 Scarovas Enforcers.

The Carriers only build bombers and the Capital Ships only build fighters.

I find this works for me

well vas sb can move but its slow, so the best thing to do is just turn around the well, keep outside of his fire, and take air superiority, once you have it, get bombers in the well and start bombing the sb

if the player isnt so stupid he will put the sb into a repair stations area, and then you can start bombing the planet

once the planet down, take it and make your own repair bays, take his repair bays down and have fun bombing the sb down

an other solution would be a kodiak hoshiko on the sb with a fightr cover, it can work with a repair bay support

a destra guardian progen and halcyon works too but you'll need at least 2 progenitors

you can also as vas make an egg with lvl 3 nano and nano the sb down while skipping shields, use kanraks to help out too and bombers

or at last the best solution for me would be to build your own sb to face it.

A Kostura cannon works too.  If it's late game, might as well.  It only lasts 15 seconds on a SB, but it is enough to give you an edge.

PS. 7 shots at once will kill any size fleet.