I agree that cost would matter.
But splitting battleships from carriers would be more cost effective, coz carrier can stay behind, and battleship can make ship-to-ship battles without bothering about it's fighter don't have anywher to land if it's destroyed.
While Collosus, even if it's cheaper theoretical mk.2 can't perform those two task separately.
for example you have two tasks (carrier operation and ship combat) that each need to take one hour.
within one hour, BS and carrier can perform two tasks, while cheaper (cheaper from BS+Ca) colossus mk.2 could perform only one.
Also as I mentioned if you lost one ship in BS+Ca scenario, it's not such disaster as in Col mk.2 case.
Not to mention two ships can be in two diffrend places, an art that single ship would never be able.
What I wan't to say is that even if BS+Ca might be a bit more expensive, it much more flexible.
....when you have an 80 Jugernauts, you would want to perform as much tasks as possible or you will be overun by shivan swarm.