I've also only cruised those, had the same fear! Loved the 8 days on the Celebration. So much to do, such a huge vessel but, they've done a great job of breaking up the venues. There are a couple choke points (Alchemy etc..) and some times elevators are tough, but overall no issues with the crowds
Going on Mardi Gras in August, then Conquest in Nov. I'm worried I'm gonna be disappointed going back to the Conquest!