Yes, you are right, dark matter,and the big bang are just the leading theories explaining an observed feature of our universe: - What is holding the galaxies t

Yes, you are right, dark matter,and the big bang are just the leading theories explaining an observed feature of our universe: - What is holding the galaxies together, given they are rotating faster than gravity from observable matter can cope with? - Why is the Universe so uniform, given parts of it we can see are outside of each others light cones? I read the OP as using the names of these theories as a handle for the effects they account for, which is fairly standard practice. Even physicists investigating other explanations do this. I'm not sure dark energy or black holes fit that description. "Dark energy" is a reference to something that is causing distance objects to accelerate away from us faster than near objects. Obviously that takes energy. Dark energy is just a place holder name for that energy given we don't have a clue what it is or where it comes from. A black hole is a name for enormously heavy, small (smaller than the schwartz radius) and very dark objects whose existence is inferred from the their gravitational effects. They are found at the centre of galaxies, among other places.