I'm not going to even attempt to answer all your very interesting and erudite questions here, simply because I don't have a week or more to spend researching and typing. And besides which, I believe you already know more on this subject than I.
But I will point out one thing that I suspect (pardon me if I was skimming) you may have missed.
There is only one Holocaust. There was only one Flood. There is only one Colosseum. There was only one Calvary. The difference is in the initial letter. It may change the meaning entirely. It certainly ignores any historical or entymological significance. If you lowercase the word (except Colosseum, which also requires then a change in spelling), you have a generic, often with a completely different meaning - related, obviously, but different.
[It is interesting that there has been no Genocide yet.]
This is not to enter into debate about Judea-Christian Fundamentalism (notice, capital F), but many religious events are thusly capped. You may debate whether the Flood occurred as described in the Bible (note the capital B), but when you see it written thus, then you know we're not talking about the aftermath of Hurricane Katrina.
Personally, to change Holocaust to Shoah would be to denigrate the significance of that event. I am quite surprised that Jewish scholars would even suggest that, as to me it looks like a type of denial.
Student or Learner