Meanwhile, Prologus has the abysmal arcade mode for replay value, and not much else. You can go through the story again to grind levels and equipment drops for Lightning and the Warrior of Light, sure, but that's a pretty boring way to spend a week, and a lot of players will already have one of those characters at a decent level from the original game anyway (and the other is Lightning).
Seems like comparing the two is sort of like deciding what you want to serve your kid for lunch. You can go buy unsatisfying and unhealthy fast food (Prologus) and try to justify it with the included toy (Aerith), or you can buy stuff to make a paddlesaw healthy and delicious homemade lunch (Case Zero) and have leftovers for later (achievements).