I would say they are too weak and need a bit more range.  Their damage output is respectable, but they die pretty fast.  They are especially bad vs the Vasari Starbase because it they don't have much time to get shots off before it crawls up and eats them.

A bit more survivability and a bit more range would be nice.  I find that in the situations where I can use them successfully, I didn't really need them in the first place because the firepower of my fleet is sufficient.  And in the situations where I need them, I lose so many that I finally just resort to carriers.

each of the ships has different issues in my opinion.

the Ogrov is a wonderful SB killer. a group of 5 or 6 of them will blast apart even very upgraded starbases pretty quickly. its pretty good against normal structures but not that much noticeably better than a carrier with bomber squadrons.

Starfish on the other hand are mediocre against SB's but will rip apart ordinary structures incredibly quickly, usually kill them 3 or 4 at a time. 

both of the ships seem too specialized considering how expensive they are. i think they should just cost slightly less. maybe scale them down by 20% in terms of credit/resource and fleet logistics costs. 

The real problem with these things (particularly the starfish) is that they have to get in range of the starbase's abilities to attack it.  The most obvious case is the starfish going up against an advent starbase, 2-3 meteors even a very large group of starfish will be wiped out.   Given their excessive cost, it makes them pretty much pointless.  You are much better off just massing a bunch of carriers with bombers for a strike force that no starbase can directly defend itself from.  

The only real solution I can think of that would make them truly useful in their intended role is to give both the orgovs and the starfish supreme range, something like ~16, so they can bombard a starbase from well outside of it's defenses.  Additionally something should be done to make them viable versus vasari starbases (which if fully upgraded will drive right over the top of them and just blow them all up).  Perhaps some sort of fire on the  move capability so they can continuously back away from an approaching vasari starbase would fix it.  As it stands, against highly upgraded starbases these structure killers just don't cut it and massing bombers just seems like a better deal, particularly because the bombers are also very effective against enemy capships, heavy cruisers, etc.

they are plenty powerfull enough. in regards to the vasari starbase: the cruisers are faster.  and the base is a victim to magnetise which is kinda evil considering this bases dies without its abilitys.

The Ogrov is powerful enough against static starbases. Use them like you would a siege frigate. Only send them in when the fleet has established superiority. I keep the fleet away from the starbase as much as possible. I use carriers with bombers against Vasari bases. Not sure about the starfish but since advent is superior with strike craft I'd focus more on bombers and use the starfish on fixed turrents like other have suggested.

I haven't played much of Entrenchment yet.  If i had to guess, I'd say that bombers although they are more versitle and also good against SBs, they also have good counters against them.  These anti-structure ships just offer another option against SBs.

So if a player/ AI decides to counter your bomber squads with mass fighters and flaks, you could switch to these Anti-structure ships.

The thing about tweaking balance is if you try to make the anti-ships too good or good enough, then it takes the strategy away from the game.  So although there are anti-structure ships, they are not a the silver bullet and neither are bombers which is fine with me.  Makes the game more interesting.  

If the Vasari SB is going after your ogrovs, then the rest of your fleet can tear it up from behind. Without frontal shields, vasari SB goes down (relatively) easily.

Ogrovs and Starfish have light armour and so are countered by fighters which is bad.

They should have heavy or very heavy armour so that planet defenses hav a harder time destroying them.

Changing the armor from light to very heavy is not a good idea because bombers would to 100% damage vs them instead of 50% damage.

But changing the armor from light to heavy might just do the trick. Light Frigates would do 150% damage (instead of 75%) and fighters would do 50% damage (instead of 200%).

This would increase their survivability quite a bit!

I agree, the attack range of those cruisers is too limited. They need an "extreme range". Countering the Vas SB is always problematic, if the range of the anti-structure cruisers is increased, they would be able to take a few extra shots before the SB is on top on them.

I think the starfish are useless against starbases.

They cost little less then carriers and have very low health.

Killing a fully upgraded starbase with 10 starfish takes hours. 30 Advent Bomber squadrons do the job in the same time. + Carriers can kill Vasari SB's and Advent SB's with Meteor, which 10 Starfish can't.

I also noticed that the attack range is only slightly higher than the starbase long range weapons.

Today I ordered 10 Starfish to attack an Advent SB. They all moved into attack range but 2 of them moved just 1 meter further and the SB started to fire its blue plasma waves on them. I'd suggest giving them a slightly greater range to counter the stupidity of the AI when moving towards targets.

In general I'd lower the costs of the Anti structure units. They are highly speciallized, but carriers can do the same and are more versatile overall. Both are countered by fighters, but the carrier only indirect (only its SC).

I used Ogrov myself recently vs half upgraded Vasari starbase.  It had 1 weapon upgrade and 1 defense upgrade, or was it 2, it hink 2.  I used 11 and lost 0 before the starbase blew up.  Very effective   He spend jsut as much on the base as I did on the torpedo frigates, and all of my frigates survived.

Only problem is that you can't take it with you to your next world

In order to get a wrecking ball Vasari SB: 3 armor upgrades, 2 weapon upgrades, 2 debris vortex, and 1 frontal shield (you can switch 1 debris vortex to get 4 armor if you care to).  <---That never dies

Subverterters don't work against SBs, but nano-bomb does.  I don't know if phase-out-of-hull can be used against SBs as I've never tried it.