The C100 is a better camera in almost every single way...but from a pure image quality standpoint...the 4K from the A6300 makes the C100 look like a camera from yesteryear.
The a6300 UHD has to be at 24p in order to get the full sensor readout and s35 image, everything else has lower IQ and varying degrees of crop, HD modes are really soft. The C100 still has one of the best 1080p images around.
To the OP, if you're looking for a video camera, the a6300 is best suited as a B or C cam to get the occasional shot if you're shooting UHD/24p, because of its numerous issues I wouldn't want one as a primary camera. YMMV.
Cheers