I have a gear that gives me 45% more damage with skills that swap to new weapon. I am using HoA build with two handed mace and lunge with dual weapons. If I build fury up by using my basic attack, and then use the hammer of the ancient, technically that switches from my dual wield to two-handed mace so I should have that extra 45% more damage. On paper this sounds extremely good, basically every time I use my skill, I get that extra 45% damage. This on their gear though, is it not what I think it is? Or is it not working the way I think it is? Can someone tell me if there’s anything wrong with prioritizing this skill. I have it in two pieces of gear so that’s a round nearly 90% extra damage with my skill.
From what I can tell, Vulnerable, Crit, Core, and Strength are still better. This seems to be better than Damage to Bleeding, Close, Injured, Healthy, and while Berserking. Mortal Draw for example provides enormous Damage Increase and Crit Chance roll
But if all those are additive damage, wouldn’t the one with the higher percentage be better, taking into account the are proc about the same amount of times? Therefore, swap damage has pretty high percentages.
Crit and Vuln are not additive, they are multiplicative, which is why you want to switch to them for your endgame ancestral gear once you get a lot of additives from Paragon.
Dmg to Close is still better than swapping weapons, since for a Barbarian it’s a condition that’s basically always true (maybe unless you play Upheaval but still).
I play Walking Arsenal and I have this affix and use Mortal Draw as well, which gives me a LOT of additive damage anytime I change weapons, which is probably like 70% of my hits. Remember though, that anytime you don’t swap weapons, you’re not satisfying the condition and not actually getting the bonus, so you should figure out if you’re in a spot where it actually improves your DPS. I use Lunging, Double Swing, Deathblow, Leap and Charge, which make me swap weapons ALL the time and also I rely on two skills to deal most of my damage - DS as Core and Deathblow for burst (so dmg with Core doesn’t work for me).
Since you’re using just Lunge and HotA you should ask yourself when it is that you’d be actually using Lunge normally without this affix, when it actually benefits you. HotA deals a lot of damage on its own (how high does it go at your level, 300%? I don’t play HotA), would you not be better off by spamming HotA for continuous, let’s assume here that it’s 300% damage, then you would by switching back and forth between it and Lunge to get that additional 90% from swapping weapons?
Let’s say HotA does 300% damage, Lunge 30%, you have 90% dmg after swapping bonus, and for simplicity let’s assume you’re making 1 attack per second, the calculations could look like this:
HotA HotA HotA 3 * 300% = 900%
(switched weapons) HotA Lunge HotA = 390% + 120% + 390% = 900%
Actually with those numbers you’re equal on damage and the second option gives you more Fury. If HotA dealt any more than 300% damage though, option without switching weapons would be stronger.
Anyways I don’t play HotA and I guess even if I did I wouldn’t remember numbers off the top of my head. 
Just look at the numbers and make the calculations yourself, but if you like the gameplay of switching weapons maybe consider going Walking Arsenal and adding Deathblow to your toolset, it’s a very satisfying (though somewhat difficult) skill to use. 
Weapon speed i suppose? 1H faster, more procs.
Not very good. Just for comparison, think of this compared to damage to core skills. No conditions needed.
And of course Vulnerable remains king in total damage output.