I agree with your first paragraph. Dark matter and all this other malarky reminds me of the arguements of how many angels can stand on the head of a pin.
However; regarding Occam's Razor, the simplest solution is that there was NO begining to the Universe. It has been here forever and will continue forever. No Big Bang, no collapsing universe, no Big Crunch, no infinite expansion (it is ALREADY an infinite expanse!)
It has evolved forever and will continue to evolve forever. It is definitely LOTS of energy, particles, collisions of particles, collisions of wave-fronts, electricity and magnetism leading to great electrical generators etc.
Read the "The Big Bang Never Happened" by Eric Lerner. Very informative.
"...the simplest solution is that there was NO begining to the Universe..."
I wouldn't argue with the premise of your statement. It takes great faith to believe either way without any proof (regardless of what science tries to teach).
But one must try to start from a fairly easily recognizable beginning to discuss alternative theories...but the first cause, the point of beginning "is" far more vast than any expanse one measures in the visible universe.
Even a singularity is infinite somewhere