I was taught that “sideslipping might help me see where I’m going”, I always presumed an oil fire would come with lots of oil, and that might be all over the screen by now. Sideslipping was mentioned, but nothing to do with the fire per se, to do with visibility.
I think the attitude was “here’s a tool, you might need it, see what happens to your screen if you do have an engine fire”.
To complicate matters further, the emergency descent I was taught was, 2 stages of flap, point the nose at the ground, stay within flap limiting speed. Does a “vicious side slip” get you down quicker, or is there a perception it might?