Okami never really struck me as a game that should be difficult and yes I know it's too easy but I'm pretty sure that was maybe the intent and that was too make sure that everybody enjoys this epic adventure without any frustrations involved with difficulty. Just sit back and enjoy the ride because the game offers a unique experience compared to anything else out there that difficulty doesn't really matter here.
Of course it could be something optional if they added some sort of toggle for it but that would just be a waste at this point to try and add something like that because it's like I said at the start of my post.
I really want to use all the weapons and abilities to really benefit me in combat, but I hardly ever use different weapons and combination. I just pick a set of combination and I can just blast through the game. I perfectly understand that difficulty in combat is not really the focus of the game, I played and beat it twice so I know that for certain; and it is without question one of my favorite games of all time. However, after you have beaten it once or twice there's almost no motivation to go back and beat it again. And trying to find secrets and stuff is really not that rewarding. They should have made something like a "amaterasu" mode or "god" mode or something like that where the enemies are much more difficult to beat and the bosses are actually a challenge. I would definitely play it more than a few times. Increased difficulty is one of the things that makes me go back and play a game again.