The Paradise is the final ship of the Fantasy Class. While the Splendor is an evolution of the Destiny-Triumph-Conquest Class (the same design as Costa's Concordia Class).
The Fatal Flaw with the Fantasy and Destiny design is that they have two dining rooms - fore and aft, with the galley in the middle. This cuts the ship in two and does not allow you to travel the entire length of the ship on one or two decks.
The Spirit Class has one extra-large restaurant at the back of the ship with the galley below it at the back of Riviera Deck. This is why the traffic flow is much better.