Not the sonic gun was OP - the shields and feed-metal was.
There is no special booster (like slow ammo or high calliber barrel)

Shadows of team 2 weren't used effectively (one time, AOE killed 3 at once).

A com which has 190 dps and 525 range costs ~4k m to morph. + 3 additional slots makes about ~5k
Grizzly, Sniper sub and 2 area shields do the same if they get about equal unit support.

BTW: Battle com with only dmg boosters on the fifth morph level wouldn't miss that often and does 30% more damage too.