It is no myth: when you compare smaller and larger format lenses covering the same angular FOV, the smaller format lenses overall consistently have higher absolute resolution, measured by MTF at equal l/mm.
Since you mention Schneider, go to the LF lens information at its website http://www.schneideroptics.com/ecommerce/C...ay.aspx?CID=162
and check the MTF graphs for various large format lenses, and then look at similar graphs for Canon and Nikon lenses. Canon here: http://www.usa.canon.com/consumer/controll...fcategoryid=111
Schneider mostly gives curves at 5, 10 amd 20 l/mm, and
- the performance at 10 l/mm is typically distinctly worse than for Canon and Nikon primes at the same 10 l/mm
- the performance at 20 l/mm is typically worse than for the 35mm lenses at 30 l/mm.
The Schneider Digitar's are different, performing fairly well up to 60 l/mm but they are not large format lenses but "digital medium format" lenses, with image circles to small for even 4"x5" LF. The only other lenses with 60 l/mm MTF charts available are Olympus Zuiko Digitals, which again outresolve the Digitar's; even the good 4/3 format _zooms_ typically outresolve the far more expensive larger format Digitar _primes_.
This is not a boast about Canon or Olympus, just evidence of the absolute resolution (l/mm) benefits of downsizing lens designs for a smaller format.
P. S. Of course others are right in saying that in practice "line per picture height" (l/ph) is probably a more relevant measure, or in other words print resolution in l/mm on equal sized prints. There I would expect larger format primes to have some edge.
Another point from earlier posts: most LF work is done at rather high f-stops, nice because the resolution can end up being mostly diffraction limited, with aberrations effects quite low. When using 35mm format allows using a significantly lower f-stop, the diffraction effect is reduced, and a 35mm format lens that gets reasonably close to diffraction limited will resolve higher l/mm. But measuring diffraction limits in l/ph, or "l/mm on equal sized prints", the diffraction limits are the same when DOF is the same.
So if good LF lenses are close to the diffraction limit, 35mm format lenses cannot do significantly better in l/ph, and might do a bit worse due to the somewhat greater aberrations expected at a lower f-stop.