Diffraction issue does not have anything with the format to do
I have to disagree.
Pixel density matters !
DLA (Diffraction Limited Aperture) is the result of a mathematical formula that approximates the aperture where diffraction begins to visibly affect image sharpness at the pixel level. Diffraction at the DLA is only barely visible when viewed at full-size (100%, 1 pixel = 1 pixel) on a display or output to a very large print. As sensor pixel density increases, the narrowest aperture we can use to get perfectly pixel sharp images gets wider.
If I read this , I would say 18MP on a 1.6 has a lower DLA aperture then 18MP on a full frame.
The pixel density is higher with the 18mp on a 1.6 ??
The smaller the pixel size the lower the DLA Aperture
What makes diffraction a challenge is the resolving power, 36 megapixel on FF is just as "bad" as 36 megapixel on medium format.
The 1.6 crop is using less of the lenses glass (resolve power) then the same lens on a FF.
So I would say the FF 36 MP will resolve more detail then 36MP on a 1.6