The way I read it…
Diablo® Prime Evil Collection contains D2:Resurrected, D3, D3:ROS, D3 Necromancer, 1 new set of wings, and 1 new pet.
Diablo® Prime Evil Collection Upgrade contains the same as above, but the price is reduced if you already own D3, D3+RoS, or D3+RoS+Necromancer. So if you already own what is effectively the “Eternal Collection”, its $10 USD more than just D2:Resurrected for the new D3 cosmetics and D2:Resurrected.
Finally if you only want D2:Resurrected, you can purchase it alone. It won’t include the new Diablo 3 cosmetics.