Ok let's examine history to determine who's correct.
35mm film vs MF film. - MF wins.
Canon 1ds vs kodak DCS MF back - MF wins. (Available on Luminous landscape)
Canon 5D2 vs Hasselblad MF backs 40MP variety - MF wins.
D800 vs IQ180 - MF wins.
D900 56MP camera vs next gen MF 120+ MP - MF will win.
This is because MF is bigger than 35mm. MF has a specific use for low ISOs and slow subjects. There is no replacement for displacement. The bigger sensor/film will always serve better in those situations.
I can only imagine what will be possible when MF will move to full CMOS tech, then you will have the pixel density of a d800 + all the advantages of MF. It's just a better tool for what it does.
Okay, that was funny!
5D MK III, EOS M3, 100-400L II, 11-24L, 70-200 2.8L II, 24-70LIS, 17-40L, 16-35 4L, 600 EX-RT, 430EX-RT, 1.4X III, 2.0X III