Small sensor fast fixed lens, Vs big (ish) sensor kit lens

Now that small sensor compacts are equipped with F 2 and even 1.4 zooms, that fall away little by zooming, in lower lighting, indoors no flash, say in a bar with lighting you can see by but challenging photographically , in that you can open up a stop or even two on the lens compared to say an Oly uFT or Sony NEX with a kit lens,  how close is the performance envelope in real world shooting? thinking in terms of a Nikon 7700,  G15 class.