In my experience, I've found three ways to deal with corvettes.
More Corvettes, Flak Frigates and Capital Ship Abilities
More Corvettes: Sounds crude yes, but if you have more corvettes than your opponent, you will obviously win.
Flak Frigates: Great way to kill corvettes and are the ideal counter. However, they are much slower than corvettes so chasing a raiding corvette force is going to be an utter pain.
Capital Ship Abilities: Some capital ships in the game have great area of effect abilities that deals damage to large groups of ships. For example, the Advent Discord can do "Scream" which deals about 200 (something close) to ships in a small area. Since corvettes have 200-400 health/shields, this will do tons of damage to a corvette swarm.
Titans also have good abilities to deal with corvettes, though by the time you or your opponent gets titan, no one should be making corvettes.
