what aperture can do for you to me is more basic. A newbie typically grabs a 18-55 kit and possibly adds a 55-250 IS. Not knowing that both of those lenses are slow ones, limited to f/5.6 on the maximum aperture. It's kind of hard to control DoF when you can't limit it any farther than f/5.6 or to understand how much more light an extra stop of aperture can get you when you never
I don't dispute that a flash is more flexible in that it can be used with every single one of your lenses (ditto a tripod or monopod). But as I said, I think a fast prime is a more basic
piece of gear. Then again, I shot with a film SLR for two decades with nothing but a 50mm prime and no flash, so I might be prejudiced.