Maybe you’re unto something, allowing 2 primary affixes on purples would justify the cost of having 1 negative affix.
It would also make it so not all cursed items have the primary affix combos you want so it would really be an item that you have to think about slotting in. It would be a good way to justify the downside of the curse and it would be a simple way to implement it.
Because as it is right now, purples are straight up better than blues in most cases and you simply allot them in your gear.
At least that was my experience, I just got a bunch of negative health curses and just added some HP stats to compensate and its all good.
Simply put:
Whites = No enchantments, 4 gems slots, 4 rune slots
Blues = 1 Primary enchantment, 2-3 secondary enchantments, 1 Gem, 2 Runes
Purples = 2 Primary enchantments, 1 secondary enchantments 1 Curse, 1 Gem, 2 Runes
Gold = 1 Special Enchantment, 3 secondary enchantments, 1 Gem, 2 Runes.
Something like that can work, and if you make gems a bit stronger then White items do retain their value. In my opinion gems should have their own effects that enchantments CANNOT have.
I made a post about it if you’d like to check it out.