The whole argument is moot because whether or not that shield is the best in the game is subjective. It is not universally accepted.

Also, I seriously doubt OP's claims of being some amazing tank if he cannot grasp this.

You say what is the point of having higher damage mitigation on blocks if you don't block often at all?

I say what the hell is the point in blocking very often if your blocks barely make any difference at all?

GLA gets 2 skills that directly enhance Block Rate. They get none that enhance Block damage mitigation.

That Serpant shield is not the best in the game. This is my opinion. You are free to your opinion that it is the shield you want most. In that case, tough luck buddy. It isn't, however, a question of balance because that shield is not universally the best option for that slot.