Dave, I think you already figured out the dry and crumbly problem - pH at drain, and to a lesser degree pH at brining. The pH is influenced by the bacteria acid production rate, as you already said in your notes on MM vs MA cultures. For jack, target a pH of 6.2 or higher at whey drain, settle and press lightly under the whey to form an initial mass. At this point, after most of the whey is drained off, you're ready to salt. pH here should be 6.0. If you miss the first target, it's a good indication of too fast of a culture or too much culture used, and it will be very difficult to hit the second target. Salt, hoop, press, and wait until pH is ~5.5, and you're done. The smooth plasticity of the paste in your gouda was because of the high pH at drain.