When should one switch to Hasselblad vs. Canon 1DX or high-end Nikon ?
Apart from the number of pixels, what do the cameras from that brand bring?
Advantages of Hasselblad medium format compared to the best 35mm systems (applies to most medium format systems):
Larger lenses means sharper optics (when measured across the whole image circle).
Higher resolution sensors currently available.
Modularity, backs, viewfinders are interchangeable allowing you to upgrade independently.
Hasselblad offers a few unique technologies, for example an autofocus system that measures and accounts for focus and compose errors.
There is the Hasselblad brand, but that doesn't completely explain the appeal of these cameras given the equally popular alternatives available (Leaf, PhaseOne, Mamiya) which don't have the same brand appeal.
Prestige, legacy or resolution:
Outside of resolution, these cameras bring very little more. They are always slower, show more noise at high ISO and do not go that high anyway, rarely autofocus and are rarely weather-sealed. DxOMark which measures cameras scientifically according to RAW performance, rates them well but sill lower than the top full-frame Nikon DSLRs or even expensive compact!
Of course there are differences beyond those but they are minor. People familiar with each system and lens can prefer the look or rendition over one camera or lens but this is due to personal preference than a measurable advantage.
Two Three Several important things Hasselblad brings vs Canon and Nikon are:
In general, Digital MF bodies (and Hasselblad in particular) swing the needle all the way to image quality, everything else is sacrificed (speed, size, high-ISO, features, etc) so in that regard you can't compare them to DSLRs on those fronts very well.
A fringe benefit is the ability to use your MF back well outside of a traditional SLR body like on LF backs. I say 'well' because you can also use DLSRs on LF backs but due to the recess of the sensor you are severely limited.
And finally, as an aside, having shot with the full gamut of Canon gear and recently higher end Nikon gear, when I had the chance to shoot with a Hasselblad for a week, the resulting images (from a quality standpoint) were amazing. There was just something more there FWIW, this probably stems from a combination of the aforementioned image quality improvements.
You can't disregard the number of pixels when considering Hasselblad, it's one of the main features, and if you need the number of Mpx a Hasselblad can offer, you would know. And then there are very few other cameras that can satisfy your needs.
We're talking about from 60 to 200 Mpx.
Then there's the absolutely huge sensor sizes which gives you a lot of things, but of the most important: more light, more detail.
Of course, the traditional reason for using Hasselblad is that it's a medium format. It's not really a fair comparison, either you need medium format, or you don't.
Leaf Shutters are a huge advantage for controlling ambient light and freezing action with flash,and the viewfinders are a lot better than canon or nikon viewfinders..
Another benefit is the reproduction of skin tones.. the 16bit CCD sensor's produce beautiful skin tones,Nikon and Canon's best camera's can also do great portraits but the Hasselblad has an advantage in producing extra tones..
Today medium format cameras are almost exclusively using Sony CMOS sensors which are excellent at high iso (better than what a smaller sensor Nikon, Canon or Sony can manage), generally offer leaf shutter lenses (except Pentax as the time of this writing), and have better characteristics such as out-of-focus area falloff, etc.. the aspect ratio is also different to the liking of many (but not everyone).
... and of course resolution and colour range (dynamic range) is one of the largest benefits of shooting medium format. D/R with todays latest MF cameras are about 15 stops. Even the last generation of MF bodies had a colour range that trounced the smaller sensor'd cameras, making whites blow later and shadow recovery easier.
The MF dslr normally has 9-11 f stops of latitude . This latitude surpasses all and most monitors cannot even view . One could practically miss fire and still get it all back . It is actually a great amateur camera because only we make these mistakes.
16 bit means 64,000 shades of a colour . 14 bit is 16,000 shades . This is alot more .
Even my old 11 million pixel 24x36 Leaf V11 gives more detail and colour depth than a D4 . The pixel depth is also more .
The more one blows up the image the better a MF one looks .