(1) YES. This particular Delta design has been the bane of many plumbers and homeowners alike. ( Most plumbers are quick learners and only make the mistake once, early in their career!).
(2) Have you removed the shower head itself to see if you get good flow just right out of the pipe? If not, then something may be lodged inside the valve body. You could try to blow it out by turning off the mains, taking apart the body, and connecting a garden hose from outside, or compressed air, to the shower arm.
Given both issues, it might be time to start looking for access to replace the whole valve. By the way, the new Delta R10000 rough in valve has eliminated the problem of the tubes, and also the problem of the nut being stuck which is how the tubes become damaged.