No, you dont need a party for Stone Sky Sea. I seem to think there was a short quest in Idyll, then the guy outside offers to fly you up and set up the dummy you want to test. And you were right, a parser is a third party program that tells you how much damage you do. But you can do that without a program. People have figured out how much HP the SSS dummies have, so beat one and divide how much damage it took by how long it took. Boom, you know your rough damage. Or just look at whether or not you can clear the dummy in question. If you didnt, you were low.