Tanks should have access to "Retaliation Damage" giving many skills/abilities or spells (All mitigation basically), including a Role Ability this type of damage: Make Tenacity (Role-Based Damage) govern that damage with more weight than all others - literally inverse for those actions the damage stats with tenacity as it works now.
Also they could modify Tenacity to weight more just for Auto-Attack.
You don't buff Tenacity to increase all damage, keep it as it is for that - But increase Tank actions oriented damage and a new damage type entirely for it's own to govern.
