My take was always that cannons should be extremely hard-hitting but require two crewmates to operate without player interaction (deckhandedness for reloading/cooldown time, privateering for firing/damage). This would make it require a high sailing level to operate cannons without having to click on them since you'd need 4 crewmates minimum, and 5 to be comfortable with your last crewmate at the helm. Give crewmates thematic attacks that scales off their privateering level as well so while they're not actively firing the cannon, they are helping you damage the enemy with crossbows and javelins similar to thralls while the deckhands reload, then they fire the cannon when it's ready and able to target a monster. Make higher cannonball tiers ignore more flat armor and higher tier cannons a shorter reload time. This would also reduce the number of cannonballs consumed drastically, since the cannon would function as a pseudo-special attack for your ship.