the interior architectural shots at f/8 are even worse; the diffraction is clearly evident in preventing additional detail from being rendered.
Diffraction issue does not have anything with the format to do, if your goal is to have a large DOF. With larger format you need longer focal lengths for the same FOV, and then need smaller aperture to compensate the DOF and - voilà - no difference. That is medium format and large format struggles with diffraction in the same way. Still people seem to use those formats, at even higher pixel counts... hmm...
What makes diffraction a challenge is the resolving power, 36 megapixel on FF is just as "bad" as 36 megapixel on medium format.
With a high resolution back you can't expect the sensor to be the most limiting factor for all your shots. Instead you are pleased that you have a sensor that max out the expensive lenses you have (probably more money in those than in the camera body) and get the most of your technique. If you think your pixels are not jagged enough for a particular shot, you can always downsize. However, fairly soft pixels both enlarge and sharpen well, so since I do prints I'm not a big fan of low rez jagged pixels a la Sigma (having no AA filter on sub 30 megapixel cameras is a bad idea (tm)).
At some point the pixel count will be "excessive", which would be when center sharpness at ideal apertures (~f/4) does not get much gain. I think that limit is around 45-50 megapixels.