Hello again! I was testing this shader and noticed that the vanilla old lighting isn't here. You see, in vanilla MC, certain sides of blocks are darker than others, as seen here:

Smooth lighting on (vanilla)

Smooth lighting off (vanilla)

This makes the terrain look good regardless of the smooth lighting settings. However, this is absent in Super Duper Vanilla, which can make the terrain ugly and potentially even unreadable in certain cases, especially with smooth lighting:

Some shaders like Complementary & BSL respect the vanilla old lighting even with smooth lighting off:

Smooth lighting off (BSL)

Smooth lighting on (BSL)

Smooth lighting off (Complementary)

Smooth lighting on (Complementary)

Granted, certain other shaders like Stracciatella and even OptiFine's internal shaders remove the vanilla old lighting, but I'm not a fan of that, and I can't seem to find an option to add it back, so adding an option for this would be greatly appreciated!

I can clarify this even further! Builderb0y says in the shaderLABS Discord, "face shading makes it so that the top face renders at full brightness, the north and south faces render at 0.8x brightness, the east and west faces render at 0.6x brightness, and the bottom face renders at half brightness. at least in vanilla."