I think we are missing several points.
The direct vision and SLR are like roadster and sedan different compromises.
SLR no parrallex, the frames are only 'correct' at the range the lens is focused to.
SLR normally about 90% of actual 35mm frame shown except e.g. Nikon F and F2... 100%
The M2, 35mm frame is near enough to 40mm that lots of people file their 40mm lenses to show the 35mm frame, note the M6 and later have different frame sizes.
You can see the M3 frame in starlight (and below) ...
The M3 focus and parrallex 'corrects' to 1m the M2 to 0.7m the SLR is dependent on lens
You cannot see depth of field with some SLR screens...
So do you like apples or oranges, most people can eat both...