The move to medium format I think should be motivated by the camera and the lenses, not the sensor. At least for us that cannot afford the latest and greatest.
Not correct. Obvious if for high ISO, DSLR is superior. Image quality will be higher with also 20MP MFDB sensors (at least Leaf, the P25 I do not know). The camera and way of working will be different.
For low ISO I am amazed at some photos I shot years ago with the ZD, which mind you was not useable in certain conditions due to a fault by Mamiya. Those shots look better to my eye than the sample images from the Nikon D800E, which look DSLR like. Good images from even ZD looks graphic and wonderful image quality of colors and sharpness, when processed right. That does not mean I recommend a ZD, of which many had same problem as I wrote of around 2007. The Aptus 22 on other hand feature exact same sensor from Dalsa but had it correctly implemented and should beat any DSLR in image quality. Pair it with a large format digital lens and it should be nirvana compared to what I mention of the ZD I had years ago. I was even using the Mamiya AF 55-110 and AF 35 in shots that I refer to, which are not known as among sharpest of Mamiya AF lenses...
Attaching a shot from Juwongsan National Park in South Korea (ZD).