The Eidolon fights are pretty easy if you make sure to use libra at the start of the battle and switch paradigms based on the Eidolon's habits. buff and debuff as required to spend as little time as possible healing. I beat odin 1st try without even realizing; I just kept attacking until I remembered I was supposed to press square.
Another reason battles might seem easy at the beginning is because the game forces you to use certain characters at different times. The game in effect chooses the characters best suited for those areas and battles. Once you have complete control over your party, those decisions will fall to the player. It will become the player's responsibility to know which characters have the right set of skills and abilities for different areas of the game. Or at least that's what I'm anticipating. I'll know for sure when that happens.
