I've been flying the Bretonian Gunboat recently and I've found it's in no way underpowered, especially if you have a friend and turret steer well. We actually managed to kill a battleship with the forward gun, since it didn't know the quick dock spot on a stationary GRN battleship, and it can hold its own very well against multiple fighters and bombers.
We were both full gun Bretonian gunboats. And they're not small either. It should probably be said that two well flown gunboats definitely equal more than the sum of their parts.
The Bret gunboats are a different class. They have massive hull and power core, and the weapon damage and range is much higher. They are closer to the Kusari destroyer than to other gunboats.