The X1 Force has a S1 Laser Repeater while the Baseline has an S1 Laser Cannon. What's the difference, and why is one more suitable to fulfill the Force's role?

Laser repeaters put a more continuous stream of fire down and are better suited for target saturation, while cannons (Ballistic and Laser) require a more precise sense of marksmanship due to their lower rate of fire. Your mileage may vary, but many people generally find repeaters easier to get used to. Also worth noting: default loadouts are exactly that. You may swap out for any S1 weapon that suits your personal preferences.