Same thing as #90 (which needs reopened), and probably a similar cause - since they're handled as entities instead of blocks, smooth lighting doesn't apply even though it should.

All of these maps are solid color, and it's clear to see smooth lighting is active, yet the lighting shown on the maps is horrifically blocky:

Entity smooth lighting was removed in 05532c6 due to the vanilla 1.17 shaders not being able to handle it, so this likely isn’t possible.

This should be labelled enhancement/feature request.