There problems with Pierce: 1. 75% hit rate compared to 100% of a shield 2. Shields can give 2 shields for 0 pip or 3 shields for 1 pip, pierce removes 1 shield for 1 pip.
To balance Pierce, the hit rate has to be increased and make it either remove 2 shields for 0 pip or 3 shields for 1 pip.
Its fine the way it is, why would you have shields if someone can simply take them all away for zero pips. Shields are there to protect you, putting them up should always be alot easier then breaking them down.