Well as far as I know DoTs all stack, but I don't know for certain. If they didn't stack it would be quite a waste of resources though wouldn't it? Things that don't stack like Hydra...well that one's quite obvious as the previous hydra disappears. It wouldn't make sense for a wound to disappear now would it?
As far as I could tell, no DoT stacks at the moment, not even Rend's bleed effect. This reinforces the idea, that these skills should be used to support your other damage skills and not as a primary way to deal damage.
Well that was unexpected! It puts a whole new twist on skills like blizzard and acid cloud; if those skills don't stack, they wouldn't be primary or secondary offensive attacks, but more like tertiary. One attack for damage, one attack for resource regenration, and if DoTs don't stack, they won't fit into either category. To me this makes them a lot less desirable, as skills that increase overall damage without being main attacks are very common, yet shouldn't take up too many skill slots. Also, does this mean poison damage doesn't stack? I mean if something does 100 poison damage over three seconds and you use it three times, once per second, surely it wouldn't do just 167 damage? It should do 300 damage!
If DoTs don't stack they actually have a unique role in your build. If they would stack, they would just become another spammable primary attack.
Well, that would be true if they had a damage advantage over the regular attacks. Using a Rend means you're not using a HotA or something, which just means doing the same amount of damage in an elongated period of time, which is just bad. Rend at least has a decent AoE to make it justifiable, an advantage that many other DoTs don't have against similar instant-damage skills. I believe buffs like Battle Rage would be much more beneficial for kill speed than most DoTs are at the moment.
Maybe. However, if DoTs don't stack then theoretically the best way to do damage is to apply a buff to yourself and keep a DoT up while using your primary, spammable main attack. That's 3 skills at least and the DoT part will require you to have a precise timing if you want to maximize your damage (100% DoT uptime) and don't want to waste resources while doing so (using the DoT again right after the previous one ended).
Meanwhile if DoTs would stack, they would be considered a normal main attack and wouldn't require timing at all, which would make creating optimal builds easier and the combat less deep.
Not exactly what I meant. I'll use an example: Flaming Dart vs. Resentful Spirit. Flaming Dart is 170& weapon damage, while Resentful Spirit deals 180% over 3 seconds, both single-target. You can have either of them, or both. On their own, you'd rather have the Dart over the Spirit because multiple Spirits won't stack.
Now, if you would have both, the Spirit would add a whopping 10% weapon damage over 3 seconds against a single target, as casting it on the enemy means you're spending that cast time not casting a 170% wd Flaming Dart. So the DoT skill is redundant because it does not add a substantial damage over the instant-damage option. Resentful Spirit is almost entirely redundant in its current form, and would better be replaced by a skill to fill another purpose.
The same redundancy seems possible in many other DoT skills: Locust Swarm seems it might well be bested by Zombie Charger, Blizzard by Meteor, etc.