I think my thought IS close to reality - actually. The most inefficient shots are actually 3 pointers. Lin is not a great three point shooter, his strength is driving to the hoop and playing PnR. Casspi and Garcia don't play significant minutes. Harden is also better at driving the the hoop, but can shoot with range. No disagreement here on Parsons.
Defending the paint is easier than defending both the paint and the 12-15 foot range. Knowing that you can just collapse and contest a layup makes defense easy. Knowing that if you leave your man to help that you could likely be burned for an easy 10 ft 2 pointer makes defensive decision making harder. It also opens your driving lanes and makes layups easier to convert. Being a Celtics fan (I presume), you have probably seen that Bass' biggest strength is his mid-range jumpers. I'd be willing to bet almost anything that his shooting percentage between 10-15 feet is better than Lin's from 3 point range.
In moving Asik, the Rockets are looking for a better front court partner with Howard. Howard needs to work alone in the paint and be paired with someone who wont crowd his space. Not many bigs shoot threes effectively, so they will be looking for a forward who has any type of shooting touch and range - aka Bass. Pair that with Bass' familiarity with Howard, his modest contract, and his hustle on defense and Bass should emerge as an obvious target.