A gunboat destroyed a fleet of snubs? Sounds fine, since Gunboats are the anti-snub shipclass. Rather than complaining the shipclass is overpowered, you might find it easier to simply adopt the appropriate shipclass to deal with a gunboat.
Gunboats, Cruisers, Battlecruisers, Battleships, Bombers and even groups of Transports can shoot up gunboats.