Complex sentence: The cancellation of "Sonic X-treme" is considered an important factor in the Saturn's commercial failure; without it, the system had no original "Sonic" platformer, and the series was attributed to the success of the Genesis.
Split into simpler sentences: The cancellation of "Sonic X-treme" is considered an important factor in the Saturn's commercial failure. Without it, the system had no original "Sonic" platformer, whereas the series was attributed to the success of the Genesis.