So am I the only one who didn't have a problem with vanilla KHII's difficulty level due to "artificially" making it a bit harder? You could basically emulate the Critical mode, in a way. What I did was I didn't use things like Exp Boost and I also limited the use of some of the other damage/defense boosting abilities when I felt Sora was becoming a little too powerful or too hard to kill + didn't always use the best equipment (especially defensive ones). I DID use all the abilities that added to my offensive/defensive move repertoire. This way it's not that I had to actively not use something like Drive forms or that I couldn't use every offensive or defensive skill in my disposal (in fact, strategic use of Drive forms was often a saving grace in boss battles and learning to guard well was essential), it's more that Sora just didn't become so overpowered as quickly as you normally do in KHII.
The only downside to this was that sometimes killing enemies became a bit slow, which wasn't too much of a problem because then you could just activate the EXP boost ability temporarily and grind 2-3 levels (which is pretty easy when you are a little underleveled) or just equip some stronger keyblade. On the other hand the fights were a lot more exciting because you really had to pay attention since you could be killed pretty quickly.
Some people complain that it shouldn't be their job to balance the difficulty and while they are right, I just kind of think some of the abilities like driving assists are in driving games. I just simply don't "turn them on" when they become available. Of course the properly balanced Critical Mode in Final Mix is superior, but this way didn't require all that much effort & stressing your brain on what you could and could not do, so I felt it was worth it for the added challenge that made it not-as-much-of-a mindless button smasher.