I keep getting my butt whooped by DLC Lightning and her comrade. Is DLC Omega any easier? For reference, my stats are max out for COM and RAV for both Serah and Noel. My monsters are Green Chocobo (Medic), Chicu (Commando), and Purple Chocobo (Synergist). Am I doing something wrong? *sigh*
Sounds like your party just sucks right now. The Lightning and Amoda fight is supposed to be pretty easy for those who have beaten the game. Maxing out just two roles isn't generally "enough" for the optional content in the game. The levels for your monsters and what skills you've infused into them will also make a difference in post-game content.
If you cannot beat Lightning, you probably cannot beat the final boss in the game. Just saying. That should be a decent benchmark. If you can beat the final boss, you stand a good chance of being able to beat Omega, but you'll definitely need a Sentinel-centric paradigm to survive his Wave Cannon attack.
Edit: One thing that you're doing "wrong" that I can think of is that you're not using a RAV monster. This works against you in this fight, because what you want to do is to stagger one of them in the battle as soon as possible (preferably Amoda since his grenades are annoying). Once you do that, you can launch with a COM and continue raping him while he's in the air. This means that you'll effective just be eating damage from the other active character, instead of both at once.