There is a skill called Runegem that appears to grant 100% block chance

There is a skill called Runegem that appears to grant 100% block chance, effectively making the player immune to the vast majority of damage.

I am not sure whether this is an oversight or a bug. If it is indeed a bug, I sincerely hope it can be fixed as soon as possible. As it currently stands, this mechanic makes resistances, armour, energy shield, and evasion feel completely irrelevant.
It can even be maintained indefinitely with just a few simple support gems. So what is the point of block chance on shields?