Those are 200mm+ telephotos. At that distance F4 makes bokeh like you'd see in a 1.8 prime. F5.6 on a 50mm doesn't let you separate the subject from the background at all, or get any light. If you are 100 meters away from something, you're likely outside with plenty of light (or shooting sports, but those guys shoot with 2.8 zooms like the EF 70-200mm f/2.8 IS).

It's hardly fair to call the 70-200 a "200mm+ telephoto". No one buys it just for 200mm or they'd buy a prime. The 70mm end is not far from the long end of an 18-55 (but it is a stop faster).

I'll grant you that you won't get extremely thin depth of field with a kit 18-55, but I don't fully agree that you can't get background separation. Distance to the lens is also a major factor there. Get close at 55mm/5.6. But more importantly, thin depth of field does not make a mediocre picture good. In some photos it can certainly help (in others it can be detrimental), but it's only one aspect. As for light, get a flash. Even an f/1.4 still won't let in light that doesn't exist.