To be fair; I have not played anything but Nightmare. So what I am about to say might not hold the same value on lower difficulty.
I think for a warrior, there is not so much "tank" and "DPS" as people think, but "Primary agro holder" and "Secondary agro holder."
No. If anything, this game got the biggest defining line of "dps" and "tank" I have ever seen.
A tank can survive about 20 arrows before needing to chug a potions. Exluding guard generation.
A dps warrior can take 4.
A rogue can take 2, maybe 3.
A mage can take 2.
A dps warrior should never hold aggro unless it is an emergency, at which you've screwed up big times. That's why you build your dps warrior as a mix of damage and control: You can keep 1 enemy locked down until it dies. Mighty Blow, Grappling Chain and Pommel Strike is enough for that.
Now, on the topic of guard in itself: It is pointless to buld for guard. For 2 reasons:
1) Guard is worthless without enough damage mitigation. Which means unless you are late-game, it's not worth the trouble.
2) The tank got 2 taunts. Your team got a handful of CCs. You should never be taking damage.
Hence I recommend building for only charging Bull as a guard generator, if you can't live without it. Otherwise go down the Weapons and Shield tree and get Turn to the Bolt and Turn to the Sword. That alone is worth more than any guard.
The reason for this, by the way, is simple: 100%(full) guard is 25% of your max health. Your mat health is probably under 1000 throughout the game(My 21 warrior is at 900). 25% of 900 is 225. 225 extra health on a full guard. So 20% is 45 health. If you taunt 1 enemy, you are surely getting hit at least once by that enemy. Now, enemies at level 4 hit more than 45 damage unless you are geared and built for it -- which requires passives in Weapons and Shield.
Now, onward. To get Unbowed you require 4, optimally 5, points. That is a lot of wasted ability points. Instead of having a rather mediocre Unbowed, you could have:
- Pommel strike + mighty strike with upgrade
or
- Grappling Chain with upgrade + Combat Roll + Coupe De Grace
or
- Turn the bolt + turn the blade + 1 extra ability point! yey!
or
- Charging Bill with upgrade + 2 points yey!
If you can't live without guard, use Charging Bull. You're going lose more health than save health by taunting enemies, and Unbowed is simply too heavy into the vanguard tree to be worth it!