Open-ended games like this (including some previous Final Fantasy titles I believe) will adjust the level of monsters based on the characters level. Does that apply at all in Final Fantasy 13-2? If so, what are the details? Does it apply to both bosses and random monsters? Is it based on how far my characters on the crystarium, or monsters too, or something else?
No there is no such system in Final Fantasy 13-2
However even with maxed out characters there are still loads of monsters who are very difficult to defeat.