This isn't in line what what others photographers (including myself) see.

Many respectable sources estimate 35mm to approach 24MP in the best conditions with specific film, 120 to be in the 40-80MP range, and 4x5 to be 100-300MP.

Tim Parkin is one of the better commentators on this subject: http://www.sonyalpharumors.com/sony-36-megapixels-vs-6x7-vel...

To address some of your other points: good LF glass can approach 70/70/50 line pairs per mm which is still really good, diffraction doesn't affect resolution as much as some people think, and f11-f16 is the sweet spot on a lot of modern LF glass - you don't need long exposures with those apertures and Portra 400, for example.