Its really just a matter of flying style. For instance, the way you fly a hwacha-fish is completely different from a lumber-fish. It requires much more pilot-to-gunner communication. That is attributed to the range (and arming time) as well as arc. Lumberjack's horizontal arc is tiny.
I will disagree that this requires more pilot skill than gunner skill. It is more even to me. Yea, it takes a good pilot to hold aim and get the right altitude and range, but the gunner has to compensate for the fact its an airship that doesnt just sit still all the time, and be able to make those extremely long range shots that it can manage.
The reason its not used in Pub games is that 1/2 the time, your gunner isnt saying anything to you. Then its like a 35% chance he's got lesmok for the long shots you need to make. I love the lumberjack, but you wont sell it as this easy thing to use. It takes practice, and fairly good gunning/piloting + communication between them to pull off correctly. Its fairly easier if youre rolling a galleon with them, ill admit, but nothing close to the ease of Hwacha or Carronade. Id also say the Flak is just as hard (effectively) to use now as Lumberjack.