Not weak, maybe un-optimized though.
I’ve been experimenting with Double-Swing builds and sadly they require more aspects, and paragon points to get going than the other builds do. Which sucks.
First off, I think Double-Swing as a Spender falls behind a great deal the other Barbarian spenders. It’s suppose to be king of single target damage but let’s be real, HoTA nukes targets faster than Double-Swing does.
My build revolved around Walking Arsenal and Iron Maelstrom. Walking Arsenal gives a constant 45% damage boost, and it was more consistent than the Unbridled Rage. Iron Maelstrom helps mitigate the Double-Swing’s inherent weakness which is AoE.
Lunge/Double-Swing, Ground Stomp, Rallying Cry, Deathblow, and Iron Maelstrom was the skills I rolled with. Use Deathblow to burst enemies and proc Berserkering and Double-Swing to sustain it. I think because we have to sacrifice a traversal skill taking Lunging Strike is an absolute requirement for the sake of DPS uptime.
Double-Swing builds require specific aspects too that you cannot aquire from Codex. You need the Encroaching Wrath aspect on a two-handed weapon so your Deathblow does 200% more damage, and Weapon Masters for the additional skill charge and a chance to stun the enemy. Deathblow has an inherently high Lucky Hit chance, and Weapon Masters pairs nicely and allows you sustain even more stuns.
Stunning and knocking down enemies is quite important with Double-Swing because it refunds fury cost. Going dual maces + concussion passive can improve stun uptime a great deal, but dual swords is also a good choice because it gives you tons of attack speed and once you solve your fury issues you can spam Double-Strike nonstop. Fury generation while Berserking, Umbral Ring, etc etc.
Get gear and aspects that are focused on making Berserking stronger and help with fury generation. Damage stats against crowd controlled enemies, buffs to close enemies, and buffs to primary skill damage. Round out your AoE weaknesses, and once you get the paragon board focus on the boards that gives damage on Berserkering and damage reduction, Carnage is a good starting board and Flawless Technique / Weapon Master are good secondary boards that give crit, damage, damage to elites, and fury generation.