Not necessarily. Kingdom Hearts 2 is one of the easiest of the franchise, even if you want to play on the hardest difficulties. If you don't feel comfortable with Action RPGs, you can choose the easy mode at the beginning of the game, and no grinding will be necessary. However, if, like me, you are a completionist, then yes, grind you must. In addition to earning a trophy that requires Sora to be level 99, you will need to defeat all optional bosses. Standing at max level helps in the endeavor.