Edit: I've since realised my very first sentence below is incorrect, making my argument invalid. But LordSloth seems to have raised a valid argument, so I'll let my post stand...
If I understand the intended balance of fleet ships and starships correctly (not guaranteed), the idea is that a cap of triangle fleet ships should have roughly double the utility of a cap of ordinary combat starships. That's reflected in the lower knowledge costs of the starships and is intended to discourage players from relying on the same basic starships every game. However, bonus starships need to be balanced the same as bonus fleet ships. That's necessary so that players who unlock a bonus starship from an ARS aren't getting a bad deal.
Long ago, bonus fleet ships were intended to be 30-50% better than triangle fleet ships. I'm not sure whether that's still the case, but if it is, it says bonus starships ought to be more than twice as good as basic combat starships.
Putting numbers on all that, the relative utilities for caps of combat ships should be something like this:
Ship cap type Relative utility
Triangle fleet ship 1.0
Bonus fleet ship 1.3-1.5
Basic combat starship 0.5
Bonus combat starship 1.3-1.5
So my question is, are Zenith Devastators balanced correctly? Here are some stats comparing them to Heavy Bomber Starships:
Stat (HBS / ZD)
Hull (Polycrystal / Polycrystal)
Cap (2 / 2)
Cap hit points (33,000,000 / 33,000,000)
Speed (110 / 44)
Range (2,500 / 10,000)
Base Cap DPS (270,000 / 340,000)
Bonus Cap DPS (270,000 / 407,983)
Special abilities (none / shoots through force fields)
So compared to Heavy Bomber Starships, Zevastators have a 26% higher base DPS, 51% higher bonus DPS (only against Heavy and UltraHeavy hulls), and a special ability. It looks to me like Zevastators are a bit better, like bonus ships should be a bit better, but not more than twice as good.
For comparison, Spire Corvettes have 88% higher Cap DPS than Spire Starships before you consider the modules.