It should be quite clear that if you want to shoot animals moving fast with lots of action, a DSLR with a high frame rate is a better choice. Nobody can argue with that.
What I don't understand are your other examples. For example, you are complaining about poor high iso performance. While it is true that the IQ180 is not a low light marvel, wouldn't the use of noise reduction software mitigate the noise down to a tolerable level? I have a camera that is supposed to be even worse by low light (an H4D-50) and my experience is that the noise reduction in Phocus (Hasselblad software) works very well. It reduces sharpness, of course, but because the camera starts with more pixels than a D800/A7r, I may even get better results in prints nevertheless.
There was also your example that the camera was too slow to operate at sunset. I have no experience with Phase One, but it cannot be that much slower than my ancient Hasselblad, can it? I have taken pictures at sunset by just putting the camera on a tripod, pressing the mirror up button and then shooting. It was a matter of seconds and I did not need a dark frame. So could you elaborate a bit on how you actually shoot, maybe we could figure out something. Maybe you could also post a link to some pictures that we have an idea (although, considering the thread as a whole, I can understand your reluctance if your pictures do not look like Thomas Kinkade on acid).
Last but not least, I noticed that you said that you have a zoom. MF zooms are horribly heavy and bulky. Maybe you would enjoy your camera more if you just took one or two primes instead of the heavy zoom. I also use a relatively light tripod compared to some, this is another item on which you could save a bit of weight. MF have a very low vibration level because of their central shutter.
Jerome, I have the SK 80mm 2.8 LS (it came as part of the package when I bought it), the 45mm Phase f2.8, and a 75-150 Phase zoom. I have actually never used the zoom (just bought it a couple of months ago). I have used both the primes almost equally, perhaps the 45 a little more.
I know noise reduction works, but one should not need to use it on an image taken at ISO 200, especially when you have to apply some degree of sharpening to most images, no matter what the capture device.
I will give you an example of the need for speed. I was in New Mexico earlier this month, driving from Bosque to Alamogordo headed for the White Sands monument. It had snowed the previous day. As I came down the mountain pass on 380 I came upon this breathtaking scene, with the little village of Carrizozo in the valley below, the Capitan mountains in the background and the Nogel and Carrizozo peaks in the middle distance. The sun had broken through the clouds and lit up the peaks while the rest of the valley was in cloud shadow. There was snow on the ground and up the mountain slopes. I was so captivated that I immediately pulled off the road and shot off several frames and a pano with my 1DX and the 100-400 MkII (the lens I had on it at the moment). I was shooting at ISO 800 to allow enough shutter speed. Within minutes the sun had gone behind the clouds again and the whole scene had changed. I was standing on the side of the road (there was no shoulder) while wondering if I was going to be run over by a truck coming around the bend. Yes, stupid, I know, but sometimes you take stupid risks for a photo.
I wished that day that I had the Phase kit with me, but, there was no way I could have gotten those shots with MF, fussing about with a tripod and all. There was no way I could have predicted I would come upon such a scenic vista either.
There are many such stories and occasions when I've had little time and that's when something like MF would be difficult to use (esp if I had a tech camera to go with it).
OTOH, I have had great moments with the MF system, shooting from a moving rowboat in Benaras with sharp results (albeit at a slightly higher noise level). Done several shoots of NYC (takes over a minute and longer for a night exposure given darkframe subtraction). Fall colors in CT were beautiful, Bermuda, Iceland, all good experiences.
BUT, everything about MF needs, nay, demands deliberation, planning. Hard to do that in every situation.