So:
1. Shields are scaled on health - that is understandable
2. ESO is multiplayer game, so it's logical that shields can be provided to group by hero with large health, i.e. tank
3. So by nerfing magicka shield you push group to receive health shields from tank - that is understandable
So why in the hell you severely nerf group shields provided by tank via bonewall (50% against 100% before patch, which can't be compensated by puny resistances PVE healers and dps have).
Random group used that synergy pretty rare before, when synergy provided HUGE shield, now they will probably quit using it at all - to interrupt your rotation for mediocre shield, what's the point...