Enchant Gloves - Mastery is 18 points. This is correct. Enchant Gloves - Haste is 20 points. This is incorrect, it should be lower than Enchant Gloves - Mastery. Enchant Gloves - Greater Mastery is 20 points. This is correct.
If you can find a Disc Priest who thinks 50 haste rating is more important than 50 mastery rating.. well, you won't. Mastery is very good for Disc Priests, Haste is a stat we reforge out of.