We Ducks are pretty well known for being three engie focused. Ever since Squash begain piloting his Galleon as an engineer, I can't think of any Duck ships without three engineers. My Junker is all about the triple engineer. It gives me two buffs, two extinguisher and two mallet/spanner combos. Its damn fearsome. However, as someone who has spent a lot of time designing my ship, I know that the lack of gunners does restrict my choices for builds. Having a great diversity on my ship is not always optimal, ie a long range merc/artemis side paired with a closer range gat mortar side. I'll never use a gunner as the game stands but that is not because they are inherently under powered but instead my play style fits better with three engineers. I prefer to sacrifice the diversity a gunner could add to my ship for the various benefits my three engis give me.
BTW the real balance question is whats better, a Gunner, or a buff Gungineer.