I've also heard the theory that the rasengan has diffeent levels of power. meaning it's much more complicated and powerful than the level that naruto has mastered. so basically, it has a lot more potential than what naruto knows so far.

Also about jutsus in general. i figure jutsu levels have to do with the more powerful techniques because they are harder and require much more chakra and control. but hey, all in all, i'm really not sure