Yeah, there's more to the Deep Sea Research Centre than just Bahamut and those dragons!
After you defeat Bahamut you can continue to descend the floors of the Deep Sea Research Centre, fighting lots enemies and solving some annoying puzzles along the way. If you make your way to the bottom floor you will find the boss monster Ultima Weapon, who is pretty tough, and you can draw Eden from him during the battle.
Seeing as you're already at the end of the game and can just draw Eden from Tiamat there's no real need to go back to the Deep Sea Research Centre, unless you're going for full completion and want to defeat every boss and see everything in the game.