I'm aware the photo quality isn't superb. The difference is a bit more noticeable on my screen. Shell icons aren't affected by this, which is why I had Explorer pinned on both screens.
APasz said that the thumbnail gets loaded and enlarged when running a higher DPI. This makes sense, so I tried setting the default thumbnail size to 48x48 in the registry but had no luck. I have a theory about it loading the 100% DPI version of the icon and scaling it up, since my Firefox only has 48x48, 32x32 and 16x16 versions; the two latter ones being way too small to apply here. I'm not entirely sure how Windows derives a thumbnail; hoping you would explain just that for me. It can't get one from the 32x32/16x16 ones, afaik.
Scrolling with my mousewheel on the desktop until I get a matching shortcut makes it slightly more grainy than its pinned counterpart, but still less grainy than its unpinned one.
48x48 and pinned.
48x48 and unpinned. Desktop shortcut still looks a bit more faded in comparison, though.
I'm running native res., ClearText is calibrated and sharpness on my monitor has no influence. Clearing icon cache and thumbnail cache has no effect.
I noticed that on all three variations of icon sizes (small, stock W10 and enlarged by StartIsBack++, aka W7 style) the icons got pixellated when not pinned. Only by changing back to 100% DPI can I resolve my issue.
I accept the fact that I have to live with this until MS decides to cater to us with Hugh Mungus screens. It predominantly affects me on my second monitor anyways.