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You guys are GOOFS, they don't do the same thing at all. just because they are both held as visible chakra in the user's hand.
Chidori = Piercing acute edge combined with breakneck speed for assassination
Rasengan = spiraling pressure over a wide area that expands and throws you with great force.
It's like a knife vs. a club. both can easily kill you. the club is larger and requires less accuracy, but it is heavier so it is harder to use. The knife is smaller and requires a steady hand to be accurate, but it is quick and lightweight.
the difference in rank IMO is based on the difficulty of learning the technique. Rasengan is a higher rank because it requires perfect shape manipulation of chakra, whereas chidori just appears as lightning.
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