I am simply comparing current-gen cameras. A crop factor is not a barrier to great low-light performance, - ( remember 1D Mark IV ), - Canon could've kept the 7D2 at 18MP and optimized low-light instead, or given us a full-frame 7D2 with ability to crop the way A7s does, - the tech is there, the will isn't.
I am mostly renting gear for shoots these days because there is nothing to buy from Canon at the moment to replace my current gear. It will be mid to late 2015 before 5D4 and 1DX2 come out, that's almost a year of waiting. I was hoping to 7D2 was going to be my solution for stills or video, but it suits neither.