>>4344938A long ass time ago, FF optics were designed with 35mm film or lower pixel pitches in mind so over-correction wasn't as common. On FF, these lenses looked very sharp and had soulful, lifelike rendering. On APS-C with smaller pixels, the flaws of these lenses were made significantly more visible. Also see: using the same lens between an a7iii and an a7rv. You can notice lens-sensor parallelism issues on the a7rv.
APS-C required more corrected glass for the smaller pixel pitches which inevitably looks flatter due to over-correction of edge CA and spherical aberration. The human eye actually has tons of aberrations and sharpness falloff which we use to estimate depth and shape, so sharper lenses look uncanny.
This is why APS-C lenses are so often the same price as FF and not half the size, closer to 2/3 or 1:1, or just shit. They're super sharp and contain extra elements.
