Congratulations on your analysis. As a 40+ year structural engineer I concur with most of what you said. It is definitely dense concrete, and the Assembly Hall roof is technically a "shell folded plate". Not many around. I don't pretend to know anything about acoustics, but do know that the multiple angled surfaces of the dome send the reflections off in many different directions versus focusing the reflections into the area of the court like a smoother concave surface would.
Those of us who witnessed basketball and hockey in the old Chicago Stadium and suffered permanent hearing loss, I can't believe there was any louder arena on earth. With all of those balconies there were over 17,000 seats in a volume a tiny fraction of any other stadium. Add to that a monstrous 3,600 pipe organ and you had the recipe for destroying eardrums.