If you want Taunt to work, make it an Aura that works like smelly and that talent that makes melee less likely to focus you.
Taunt: While active, enemies within your range are more likely to target you. Also, enemies inside the taunt aura has a chance to deal less damage to allies.
I like this suggestion. EDIT: ...but the simpler solution is still to just not have it blocked by armor.
This game's balance is skewed by the fact that AIs will stop at nothing to CC the glass cannon, heal 'masked' undead without a care in the world, and ignore the tank completely. The purpose of taunt doesn't have to be to turn the fight into an MMO-esque tank-and-spank, it should simply be used as a way to give squishies breathing room, and to enable builds based on retaliation, shackles of pain, etc. Because, right now, there are more worthless skills and builds than there needs to be solely because the AI doesn't give them even a small iota of space to function unless they have literally no other option.
Yeah, it turns out that sometimes just making the AI smarter isn't the best way to go. It's better to make AI that is a little less smart but a little more fair, instead of one which is very "smart" which really means that it cheats.