I am playing on legendary skill level and have a hypothetical sword that does 90 damage and has a 30 pt absorb health enchantment. It is my understanding that because of the level the sword will only do 30 pts damage to the enemy but what about the enchantment? Is the enchantment scaled down to 10 pts damage from health absorb? How much health will I absorb when I get a hit 10 or 30?

your 90 damage sword will deal 22.5 or 23 damage. I think your enchantment will still be 30.

Nope, the enchantments go down too. Everything is lowered, literally everything.