Having flown more than a few carronade fish myself, I can tell you the carronade is not high risk high reward. It is incredibly easy to stay on a target, the only thing you have to worry about is their teammate coming in for a 2v1 which shouldn't be happening if your teammate is doing his job. They're also surprisingly long range, once that balloon is teetering on death it doesn't take much to keep it dying. Your reward, on the other hand, is the slowest kill ever. Much like how hwachas take forever to actually kill a target, it takes AGES to take down a competent crew that doesn't want to go down. They won't ever rise above you, but they sure as hell will drag it out for ten minutes.
We don't always play the same matches so we will have different perspectives. For me it becomes high risk to charge long range barrages from good gunners, and high reward to lock that long range vessel in a dive toward the ground and effectively being forced to survive. Staying out of gun arcs that can disable your gun is the part that gets tricky.
And yes, it does take ages to kill someone on your own. Thats why its not OP. If it did, then you could disable them and pop them rather easily. Currently, your ally has ample time to assist, but if that time runs out, thats on them.
I've got to go with Zill here. Properly positioned teams can often make it difficult for a carronade goldfish to even approach.
When it does a good gunner can often break the enemies carronade before the balloon is fully destroyed buying time for repairs and repositionning.
If you do get balloon locked, two crewmen working on the balloon, maneuvering behind the carronading ship, drogue chute while descending and a quick hydrogen when it's up can often get you right back in the fight.
If that still isn't enough, a good teammate can save you before the longest kill ever finishes you. If you're situation isn't dire, your teammate may be able to kill the other opponent and get you out of the lock. Or they can decide to directly shoot at the locking goldfish while tanking the other enemy shooting at them.
There are a lot of options to go against the strategy, however in an unorganized pub game, one good carronade goldfish can often single handedly disassemble an uncoordinated team.