Well,
Sony seems to know how to make good pixels… Phase One, I don't know…
I have a P45+, it is still in the 10000$ (US) range and I don't know if it is any better than a 2000$ Sony Alpha 99 of 2012 or a 2000$ Sony Alpha 900 of 2008 which I also happen to own.
I have no doubt that the IQ-250 delivers, as I have seen evidence on it. On the other hand, I know that the 41 MP phone cam does deliver, as I have seen evidence for it. Stefan Steib, the man behind the Hartblei HCam is quite impressed by the 41 MP phone cam. You know, it has a Zeiss designed lens with all aspheric elements designed for it.
My take is really that I enjoy my P45+, but the Sony is better in all aspects except resolution. Ask for any parameter except resolution and the Sony is the winner. I shoot a lot with the P45+ on my Hasselblad 555ELD, because I enjoy it. But Sony wins in all aspects except resolution, and
the simplicity of the Hasselblad.
A way to put it: The Hasselblad with the P45+ is fun to shoot, but does not make great pictures. The Sony Alpha is functional and makes great pictures, less fun but more functional.
For the best image quality I would go with a technical camera with an IQ 280. If I wanted the best results, I would go with a technical camera and the IQ 250 and use live view focusing. Or I may go with the Pentax 645Z.
Would I need the best image quality at reasonable price, I would go Nikon D810 with good lenses.
But, right now I am shooting with a Hasselblad 555 ELD/P45+, and a Sony Alpha 99, being quite happy with both. But, the Alpha 99 is the more functional camera of the both. By the way, I also shoot a Sony Alpha 77, which I use for street and wildlife. The Alpha 77 has smaller pixels at APS-C frame size. I can shoot 400/5.6 on the Alpha 77, or 400/5.6 with 1.4X extender on the Alpha 99 at f/8. Results are to bee pretty similar.
Best regards
Erik
This of course assumes all pixels are created equally. If you believe that I have a 41mp camera phone to sell you .