When you get hit by the Chidori, one of the damages you get is you get electrified since it's made of electricity.
What about the Rasengan? Since the Rasengan isnt made of electricity, what's the damage it's supposed to make? Does it burn? Is it sharp and by rotating you get cut? I discount that the damage comes from the impact, because since it isnt thrown many times and it isnt propelled, the damage and inertia of the Rasengan would be similar to a punch, and it wouldnt make sense to create a technique that does the same damage than a punch.
What's the destructive power of the Rasengan about?