Get a Bastilla led Jedi team, keep them just a touch behind your arena team, and you'll be able to cruise thru GW almost everyday. Bastilla led Jedi are a natural for GW because their protection up is fully recharged before every battle. So as long as you keep them alive, every battle is a fresh start. Even when some of them had their hp eaten into in the last battle, it'll take the opponents some turns to get thru the freshly recharged protection bar in this battle. They will have been fully healed by then.
Also I think the opposing team power distribution has a global balancing factor. For example, if you run into some particularly tough teams on N6 and N9, it's likely that N11 and N12 will be a lot easier. Conversely, if you cruised all the way to N11, well N11 will most certainly be a nightmare.
