For the twilight defender, why isn't the sword dusk enchanted with the silent moons enchantment (deals extra damage at night)?

Because the Silent Moons enchantment doesn't deal extra damage at night

??? But, isn't that what the enchantment does?

It's broken, no damage whatsoever from the enchantment Shame, that enchantment always interested me.

"• The Silent Moons Enchant is broken. While targets hit by a Lunar-enchanted weapon will glow as if the effect were working, PC testing via developer console confirms that no extra damage is done. Analysis of the game files reveals this to be due to the enchantment targeting weapon speed and not health. • This bug is fixed by the Unofficial Skyrim Patch." From the UESP.

To be fair, they said the same thing about Tower of Strength. But yeah, I think this one is actually broken.

I heard it affects 'WeaponSpeedMult.' I'm not sure what that means

Why don't you just put, "for those who have Dragonborn, use Bonemold armor (regular, guard, or what ever the other variant is called). For those who don't have it, use dwarven"?

So many variables.