This build is really for max endgame raid DPS so it’s all about squeezing that DPS as high as you can. 20 Barb is plenty viable, but doesn’t perform as well in that role.
The FvS trance is better for a couple reasons:
-You can get you Cha higher (razorclaw is -2 int, and there are more Cha racial PLs
-it gives bonus to Attack as well as Damage
-and most importantly it’s only 3 AP and this build simply does not have enough AP for Harper trance. By the time you pick up razorclaw Crit multi, vistani capstone, and then either Kensi or FrBerz T5s, there just isn’t enough left for a universal trance. (This build uses just about ALL the extra AP from racial PLs, Tomes, etc.)
So you need 1 FvS for trance, then it’s just a matter of what to take for that last level. Warlock is nice for those passive arcane warrior stacks and gets the best damage increase for those longer raid boss beatdowns. There’s other options too that work just fine. I would sometimes forget to turn on the warlock aura, and the build still hits plenty hard lol