Great thread! I very much appreciate the engineering and pragmatic approach, with math and physics to back it up.
If this detail was in buried within, I missed it: As to finish leveling the concrete pier top, a quick check shows some self-leveling epoxy resins show compressive strength ranging from 3900 psi to 7500 psi depending upon compound. That's JB Weld territory at the lower end. This should be sufficient to resist (significant) deflection in the mount, yes? I realize the mount needn't be level to achieve PA, and a proper GEM won't care much.
Short answer: yes.
I have reasonably big gear: a Mountain Instruments MI-250 (65 lb), a 14" classical Cassegrain (55 lb), counter-weights (63 lb). Even if my pier plate was 1" x 1", that's only 183 psi...