Yes, I have always thought that all the things you loose with small MF are far from compensating the very tiny image quality advantage. ...
Now, the 100mp sensor will of course be superior on the Fuji once it is released, but investing today in the 50mp MF sensor doesn't seem reasonable to say the least.
Of course the sensor age gap is a major factor, so let use see how the 100MP 44x33mm sensors perform — with comparisons perhaps now including the multi-shot super-resolution modes of some Pentax, Panasonic L and even Olympus bodies!
As far as sensor size, here is a fun fact: the sensor area ratio from 36x24mm to 44x33mm is about 1.68x, more than the 1.5x from 4/3" to Canon's version of APS-C; a hair less than the 1.7x from 4/3" to the 24x16mm of the Sony-Nikon-Pentax-Fujifilm version of APS-C. So is the 1.5x to 1.7x gap too small to offer an IQ advantage to 44x33mm over 35mm or for APS-C over 4/3", or is it big enough for those larger formats in each case to have worthwhile intrinsic IQ advantages?
P. S. The DPReview argument about lower usable ISO speed on the F850 is rather bogus; they look at the lowest ("normal") exposure index settings of 100 vs 64, ignoring the that these are not (and should not be!) the same as the base-ISO speed: as has been discussed numerous times, different makers simply choose to have different amounts of highlight headroom at their minimum normal ISO speed setting.