damage is variable, range is variable (boosters)
weapons should differ more in alpha, aoe, projectile speed, etc to not become redundant.
The riot gun doesn't help you against raiders surrounding you.
A sunburst commander with enough buffs to penetrate shields cost 5k m (skuttle will hunt you!)
Sniper coms shot both weapons at once (and do sometimes a lot of overkill).
But I think the main reason why nobody uses some things is, that the dual-weapon boosters (auto-flechette, etc) are too different.
It is too complex to compare weapon setups, especially duals with a lot of specific buffs vs 2 different weapons which are more versatile (dguns vs dual-setups)