What benefits does a S7 cannon give you over multiple smaller weapons with the same DPS? Does the larger weapon have higher armor penetration, range, etc?

Larger weapons do more than just higher damage or DPS, they also tend to have higher penetration rates (when physicalized damage comes in) and the weapons themselves are more durable, with enhanced resistance to distortion and damage. As a result, the DPS of a single S7 may on paper be equal to multiple smaller weapons, the increased range and penetration provide a significant benefit against certain targets.