Just stating facts MC.
I love Frank Lloyd. He was one of the best. As you noted, Falling Waters needed millions to restore and reinforce its structure, or else it would have literally fallen apart and into the river below it. Same thing happened to one of his houses here in the Cleveland area. I knew personally the Architect (now deceased) who’s job was to save that one too. Interesting fact, in most municipalities back then, obtaining building permits and the review of structural and the overall integrity of residential homes was almost non-existent. Not so today. Much more is required from permitting and conformance.
Yes, it is interesting that fire rated walls and STC conforming walls actually combine in doing the same but different jobs. For example, it would also be more wise to use Type X Drywall for sound, as it is more dense. Why? Because Type X is a fire rated drywall/ gypsum board. But it can benefit sound separation as well.