Hi,
Per your own admission, "Every extra mm of coverage demands more" So the comparison is fair. Granted, as I stated, the Nikon and Canon offerings are faster, much faster, but they are also far more expensive. In other words, the entry by Fuji is competitive.
There is no such thing as Full Frame MF. It's just marketing speech. For a long time, 6 x 6 was the preferred format (about 56mm square) for many cameras, but 6 x7 was also very popular. On the other hand, I agree that P1 Business model will be better served by a "large sensor" MF, not even a 56 x 41.25mm but close enough to the arbitrary 645 for the marketing department to say "first full frame MF mirrorless" or whatever. Hasselblad was very limited, in financial terms when they developed the X1D (thus I don't believe the lenses will cover larger sensors, but if they do ... ), and Fuji's MF is their FF 35mm replacement. So it could be a differentiator for P1.
Best regards,