The torp option on the Void Stalker is unofficial by the way. And too claim there are 2 Pirate battleships I don't understand it when you say the Craftworld has 4. The torp option does not give a new model so to say.
Yeah, the Craftworld has 4 basic models (Flame, Dragon, Wraith & Shadow). (Corsair: 9).
And indeed the cruiser (or escort) vary by the fact which weapons you give them and in which combo.
But look at the Imperial Navy or Chaos cruisers: a core model (1 !!) with various weapon combos.
Corsair Eldar
Void Stalker (1 model, 2 game variants, 1 being unofficial)
Eclipse (1 model, 1 game variant)
Shadow (1 model, 1 game variant)
Aurora (1 model, 1 game variant)
Solaris (1 model, 1 game variant)
Hellebore (1 model, 1 game variant)
Aconite (1 model, 1 game variant)
Nightshade (1 model, 1 game variant)
Hemlock (1 model, 1 game variant)
Craftworld Eldar
Flame of Asuryan (1 model, 1 game variant)
Dragonship (1 core model - with 4 different weapon combinations, 4 game variants)
Wraithship (1 core model - with 4 different weapon combinations, 4 game variants)
Shadowhunter (1 core model with - 2 different weapons, 2 game variants)
In the rules doc they could have made a separate entry per Dragonship variant but they didn't. The IN cruisers are shown separate but could be potraited the same as said Eldar ships.
So, I agree that the Corsair have more variety shipwise / core model but variant wise it is quite even.
http://www.epic40k.co.uk/lib/comp/gothicomp09/gothicomp104.html