First of all, it seems to be a very impressive lens. If, someday, I am sitting around with piles of money, I'll definitely trade a pile for an Otus lens. Hopefully by then, they have a wide angle Otus, as that is where I see the MF being less of an issue.

In terms of pure resolution, it definitely seems to be the king of the 50 mm lens, but overall, I'd still put my money on the 300 f/2.8 II or maybe the 200 f/2 as the best overall optics. But the Otus seems to be in that company of the very best of lenses.

Regarding the question of which is the limiting factor in overall resolving power, the lens or the sensor, it does seem that the lens is still limiting somewhere between 21 MP and 46 MP. Based on the images I've seen, there is still something to be gained with good lenses up to the 36 MP of the D800/a7R. Not that I would consider that to be the ideal sensor size. Too many other factors go into that. But, with good lenses, they do seem to be able to resolve more detail.

Also, in terms of how Bryan runs his tests, I believe there is also a slight issue in comparing APS-C and FF. Because he fills the frame with the ISO 12233 chart, the crop sensor camera is actually physically further away from the chart than a FF camera. So, a 46 MP FF camera positioned the same distance as a 21 MP FF camera would likely resolve more detail than the 46 MP FF equivalent 18 MP 60D that Bryan used in his tests.