When used to remove System Strain, the Damage Control action can be done repeatedly by multiple crew members each turn. Doesn't this mean that using small numbers of Ion Cannons against something with large crews is pretty useless?
Not even going to the Star Destroyer level, consider the Wayfarer. Even after accounting for pilots, copilots, gunners, etc. the ship should have five or six crew able to wander about performing Damage Control every turn.
Sure, Ion Cannons are great for disabling fighters without destroying them, but I seriously doubt their utility against ships with larger crews unless the amount of ion firepower is overwhelming.