Sorry if it has been said before, but I don't think tanks are gonna have to gem all Stamina. I'm pretty sure blizzard stated that bosses are gonna hit for less per hit so tanks can take multiple hits but that healers will have to heal multiple times to bring back your health to full. Gemming for avoidance might overcome stamina if healers have to deal with mana. Gemming for stamina was there to avoid beeing 2-3 shotted by bosses on an unlucky streak.