I think it depends of what content you are aiming, these days Hard Mode is pretty easy and can be done solo tanking or a dps acts as a tank midfight. As an off tank for this trials you could focus on being a DPS tank.
If you are doing extreme content, there is a specific role you'll required to fullfil, tank chirada, voke spiney, switch at 2 stack debuff, take adds, be close to a dps to not diminish his dmg.
In any case, always have some accesories which can change your vit-dmg settings.