I think the bit about characters of different ethnic backgrounds but US culturization makes the point -- much of this has to do more with
cultural familiarity rather than 'race', ethnicity or something such as skin color which of course can be quite varying even within one family! -- it's far easier to create nuanced characters on the background of cultures you're familiar with.
As a writer with some self-criticism we will not be wanting to create for any central role, a cardboard cutout 'ethnic' character constructed from stereotypes, assumptions and half-knowledge. Neither for readers nor for our own enjoyment. As peripheral characters they might be ok...
So it's easier to stick with what we're are confident we can write about with convincing, natural immersiveness. In creating a character with foreign roots but local upbringing, one can use some surface knowledge of that foreign background together with deeper knowledge of the various prejudices and assumptions existing in our own cultures to create a realistic, individualized character with some tension in their identity ... while using only surface knowledge of a foreign background to create a core character will run the risk of creating a cruely hewn standin for a group.
Of course it's possible to subvert this with self-aware, tongue in cheek usage of stereotypes. But an example you can note here on the site is that there are some people who have researched the Romans to such a degree that they can create an immersive illusion, and the roman aspect really feels like a proper background and setting ... but there are also stories where it's just cookie cutter stuff....
I find that especially in images - most extremely in 3D computer-rendered images - the tormentor(s) are ridiculously reduced stereotypes. If there are several of them they tend to be clones of the same bald expressionless hulk.
Now of course most of the creators of these images are guys, who usually focus their creative energy and attention to detail on the female victim; it's only a minority of them who dare to portray the tormentor as 'actually the very person of themselves, the author' -- instead the tormentors are more often generic representations of amoral sexual energy -- comparable to the 'headless dicks' you'll see in porn
-- and in that case making them the cultural '
Other' is probably an easy decision driven by the subconscious.
Especially if the creator harbors some pangs of guilt about fully identifying with his impulses which seems to be a quite common phenomenon ... in that case it's easiest to just go for 'othering' those manifestations of the dark aspects of his self, which will be seen as 'uncivilized', 'raw' etc, and for the average white guy that can easily be the bald black muscle-hulk who will stand in for a stereotype of 'untamed barbarian sex drive'.
It's important though to recognize that it's not only 'white people', or the European-derived cultures associated with that appearence, who are capable of harboring stereotypes; other groups also assign distinct sexual stereotypes assigned to certain instances of 'The Other' from their pespective, and if you dare to look at the sexual fantasies created in other cultures, such prejudices can also be quite obvious.
For my taste the tormentor should introduce himself, not inevitably as a man of wealth, but always of taste, with a reason for what he does, and no matter what his origin and extraction, a disciplined master of himself so he shall better be a master of others, and not just some hulk or golem.
Well compared with other stereotypes the Nazi stereotype, especially if you're talking about the SS, Gestapo etc types, are guys who consciously signed up for the dark side. Also instantly recognizable iconography is always useful to get a story up and running quickly... Nazis, zombies, and vampires are always instantly recognizable and out of those the Nazis are the only ones who actually chose their look themselves