yeah....you dont have to see it kill someone to know its capable of killing someone (actually it DID kill that fake akatsuki guy that posed as itachi)

Kabuto's healing ability saved him from dying to the rasengan, and probably would have saved him (and without using up as much chakra in the process) if it was a chidori used on him as well. And yeah, fillers don't count.

The difference between chidori and rasengan is a bullet and a bullet that explodes on impact.