they are however really easy, so for less skilled crews it can give an advantage.
Again ignoring the fact that there is a difference between a weapon that relies on gunner skill and a weapon that relies on pilot skill.
Carronades are easy for gunners, harder for pilots. It balances out.
At this point I'll even throw in an exemple:
Let's say you are on a long range ship, like a galleon with lumberjack, flak and mercury. As a gunner, you have your work cut out for you, you need to make every single shot count and you have to hit the relevant components at long range. As a pilot you just need to be aware of your surroundings and position yourself accordingly. Once your gunners have a clear shot your only job is to avoid throwing off their aim, usually by parking somewhere and letting them kill stuff.
Now let's take the carronade. As a gunner, it's easy, very easy. You only need one kind of ammo basically and the balloon is often the largest target on an enemy ship, plus you are going to fire at short range. As a pilot you need to carefully plan your moves, ambush the enemy, rush in when they seem distracted and once you have their balloon popped you still need to manouver all the time to keep them in a good position to not only keep their balloon down but also dish out some damage with another weapon when their armor goes down either because of carronade shots or because of impact with terrain.
See what I mean? A gun can be easy for one class, harder for another.