Holocaust has been used and was understood at least since 1189 to describe the burning of Jews. See my comment

Edit: this is btw. not to detract from your point. The word holocaust as the deliberate burning of people was mostly used for burning jews, but also witch-burnings and similar events. Even the great fire of London was called a holocaust.

In pre-WWII parlance, calling what happens in Gaza a holocaust would absolutely be appropriate. Post WWII its usage is just… not helpful and has bad connotations that detract from what is important in the discussion.