>>1569341I found the numbers for various sizes of both. The numbers are so surprisingly close, the biggest difference I see is geometric accommodation for 26" and 700c wheels. Other than that, the larger sized 20 is so close to a size S with the exception of longer toptube on the cannondale because frame size was meant for bigger people and taller standover on the canyon because bigger wheels.
My conclusion? 90s rigid is pretty much a gravel bike except the sizes and geometry is shifted a bit because wheel size.