While memorization is a lot of the fights, there are several aspects that help me not feel like it's the only thing that matters.

The first is that when you get to higher difficulties, there are often one or more mechanics that require real time problem solving. Even if you have the solution memorized, you still have to untangle the strings fast enough to resolve it. The second is that I enjoy improving at the fights. Even if I can do them, there's usually something I could have done better than I can work on next time. That turns my focus from the parts I have memorized already to the parts I can improve on. The third is that I have a lot of friends who either play the game or who I met while playing the game, and when we really do have fights down that much, we can chat and have fun while we're doing them. If we're grinding an EX so we can all get the mount, we can just chat and have a good time the same as you would running treasure dungeons or doing dailies.

edit: syntax