Again, only very top tier gunners can drop a ship's armor with one clip of gattling fire, it's a difficult skill, and without it a quick kill turns into a long kill.
Well, let's look at numbers.
The Gatling deals: 10 Piercing and 10 Shatter damage per shot.
On the armor, that is: 15 Piercing damage and 2 Shatter for a total 17 damage per hit on a ship's armor.
The Gatling has 60 bullets per magazine, so assuming you are actively looking to hit armor only, it can deal a total of 1020 damage on an enemy's armor. Assuming your whole magazine goes into the armor and no components.
Even if you take components into account, that is still more than enough to take out any ship's armor even if you miss a lot of shots, unless you are aimming at a Galleon or the Junker, both of which have their componenets set up in a way that they can easily absorb some damage and one being extremely slim.
So no, I don't believe it is a great skill, it just takes a minimun ammount of practice if your pilot doesn't turn around at full speed all the time like a drunken idiot, then even an average gunner should have no problem taking out a ship's armor in less than a clip, heck, I'm not even top notch, but I can manage to do it easily.
The only ships that have armor even close to match that tremendous number is the Galleon and the Junker, one of which has 800 and the other 700 armor and that's still at least a 200 damage difference. meaning, those ships are the only ones that can legitimately avoid having their armor reduced to nothing from a single gatling clip (One mallet stroke included which means +250 more damage needed). On every other ship, your armor is hilariously exposed and that's only assuming you are only getting hit by a gatling mind you.