The thing is, every shield has a "momentum, psion, poison, steal, deflag, etc" weakness + its own unique weakness. Wings let through flying attackers, Gravity Shield lets through >5 hp, Dissipation can die out... All of these have an extra weakness that allows one to be damaged in some way.
Except for Dim shield. This is why I think its unfair.
Some say the 3 turn counter is its weakness, but thats 18 turns in a chain, more than enough to end any game.