Makes sense to me. Trying to be "the same as Nikon, but cheaper" is a losing strategy. This -- making the best full frame camera, and charging top dollar for it is a winning approach. If they come out with big megapixels and fix their low ISO noise issues, they have a winner.
Re why not get a medium format -- the short answer is versatility. They are counting on the all-rounder/jack of all trades winning in the long run.
For example, what if you want to use it at ISO 800 or higher ? What if you want to use it with a lens like the 70-300L or the 400mm f/2.8 ? What is the equivalent lens for medium format ? (and again with telephotos, consider the limitations on ISO, reach and aperture) What are the medium format equivalents of a 24-70mm /70-200mm wedding shooters kit ?