I don't approve of mixing sandwich meats. Unless you are adding sliced turkey. You can add sliced turkey for the same reason you can add water to stuff.
What about bacon cheeseburgers? Does that constitute mixing of meats? Or the Italian sub or Muffaletta?
Are we sure there are really 8 different meats from Arby's? Or just the same meat with different food dyes?The meat combination is good for noodle dishes.
In my younger and less health conscious era, I was happy to mix pastrami and corned beef on sandwiches all the live-long day.
I don't think of a hamburger as a "sandwich", so I guess I need to be clearer with my definitions. Let's go with "sliced sandwich meats"