That’s gameplay, not lore.
The question being asked is which capitals ‘in lore’ would be difficult or easy to siege. In gameplay, yeah, the Alliance gunships don’t need to go back to refuel or get ammo, they have an infinite amount of them because they’re staying up there as targets for a quest.
Same in the Jade Forest, the Horde gunship has a mini-gun style weapon that has infinite ammo and the Alliance gyrocopters have infinite ammo/rockets for their weapons, with the only thing limiting them being cooldowns. In lore neither of these things would be true and the Horde and Alliance would need to be very careful with their targets.