I still haven't finished AC. It just didn't grab me. I'll need to get back to it at some point.
As for the XVI DLCs I didn't think they were any harder than the main game, and I played them on Final Fantasy Mode. My biggest problem with the whole game is that once I found an optimal build there was really no reason to try any other abilities. I played through the entirety of FF Mode with that same setup and was able to handle everything without too much trouble. Every fight felt the same. I only tried other builds late in the game out of sheer boredom, and sure enough they weren't nearly as efficient as the one I was using.