Err, not necessarily.
First, your standard weapons are usually much better than cannons, at least the non heating kind.
MUCH better, unless you are trying to sink an enemy ship.
Second, the heroes may not risk firing overheated cannons due to explosion, which means they are often only firing the overheating cannons every second turn (and indeed, the primary reason for firing a cannon with a dark charm is to explode it). A Dodge is often a better option than an Aim, if the enemy is firing back - or the hero has to move into position due to knockback etc, or one hero is serving multiple cannons.
Admittedly, most of this is conjecture on my part - our encounters have very rarely included ship to ship battles (so little need for the cannons) and when they did the heroes were vastly outclassed (including an ambush where the OL ship started the encounter across the bow and could not be targeted by hero cannons) and fled ASAP.