You can hit hull, balloon, both turning engines, and run back to hull right as mallet cooldown ends, so it's not too far from everything else until something breaks. In that case, the pilot and/or gunner can help if needed. Trifectas are not easy on the junker in practice. You have to angle your ship just right and sit still to avoid awkward diagonal movement. It's not just a matter of arcs. The Galleon, Mobula, Spire, do trifectas effortlessly, so no, a trifecta is not much of strength for the junker. The Pyramidion is also capable of it. The hull sweet spot, a gimmick, should not be essential to a ship's success. I, and I believe the original poster, are not discussing highest level play so I don't care how useless you might find the gunner class or some supposed one only viable build.
If you're not using trifectas, why use a junker? Without a front engineer you're just a crab pyramidion with an odd balloon.
Oversimplification. There are clearly advantages and disadvantes to Junker compared to Pyramidion without concern to trifectas. I shouldn't have to elaborate.