That's actually not particularly OP. I mean it's good enough but when you realize how it would be in practice it's just okay. I mean I like it but it's most definitely not OP. It actually makes WAR more of an OT role, which it's been a MT role for a long time due to how easy it gets aggro and can swap into dps stance.

But MT or OT, in savage you CANT just blow you CDs all at once. Every one requires both tanks to have CDs for mechanics. So a 4% aoe shield every min is actually just right, I'd say. At most you'd get 2 20% shake it offs in maybe o2s, that's it. And in casual content a 20% shield doesn't really matter anyway and will help not so great healers so it's not bad if it's true.

I assume Thrill, RI, Vengeance and maybe rampart would be consumed. Seeing as two of those skills have 2 min cds, it doesn't actually have the full 20% every minute. It would be 12% every 90 seconds or so.