Well, aggro works in 2 ways. Proximity and aggro generated. A wizard or someone can have much higher aggro generated than a warrior and not have aggro because they are not close enough for the mob to give a shit. So, if taunt is +1 and a caster has a few hundred over the tank but has not yet taken hits, if the warrior taunts then he just get a few hundred +1.
I don't play a warrior but sometimes on my druid when I'm nuking and my monk is tanking, if I go up to melee on Zorcid he will take hits.
I don't play a warrior but sometimes on my druid when I'm nuking and my monk is tanking, if I go up to melee on Zorcid he will take hits.