Folks are comparing AREA, rather than comparing the LINEAR differences between format sizes. And if you compare the Vertical (short) dimension, you can equalize the differences in aspect ratio. Using 8"x10" print size as a common size (1.25:1), the short axis is fit to the 8" dimension, and the aspect ratios are clipped on the long side to fit the 10" dimension of the print.
- APS-C 15mm: FF 24mm = 1.6x linear
- FF 24mm: 645 43mm = 1.79 linear
- FF 24mm: 4x5 93mm = 3.875x linear
- FF 24mm: H6D-50 32.9mm = 1.37x linear
As evidence that this is the right technique to compare, in comparing the MTF scores of lenses for different formats (e.g. 4x5 format vs. 135 format) lens manufacturers have always compared the line-pairs/millimeter spec and factored in the final enlargement magnification to result in line-pairs per millimeter delivered to the same 8x10 print. 24mm 135 frame needs 8.5x enlargement (linear magnification) vs. 4x5 needing only 2.2x enlargement, so starting with 85 l-p/mm on a 35mm lens still results in less resolution on print than 50 l-p/mm from a large format lens:
10 l-p/mm vs. 22.7 l-p/mm, which is why some publications insisted that they only publish images from 4x5!