True, but they aren't always KOs. It doesn't even deal that much damage, so if anybody is good at using the air-dodging mechanic Sonic's Final Smash is useless.
It deals around 15% per hit, but it usually KOs at around 60% for me, so it's not a huge deal. But yeah, you need to be good at air-dodging when around Sonic, especially during his Final Smash. =P