The damage reduction is a double-edged sword since your opponent gets it too. For the upped, I judged that a 2-point damage reduction was more effective, since one of the uses of this card is to replace your enemy's shield with an inferior shield. Upped creatures, particularly upped light creatures, should have no problem doing significant damage through the enemy's 2-point shield.
The unupped is expected to be used more defensively, since a 2 damage reduction shield is pretty good for unupped.