I have 6 phantoms up wihtout any DA, I don't see how 250 DA can benefit to more dps compared to 250 stats in crit dmg or determination.
I really hope you don't suggest players to run dps spec for pvp, it's guaranteed oneshots on them?
Yes I was confused what you focused on for this guide, a build for both gameplay aspect usually fails and is not so reliable on since you defo miss out on stuff if you'd dedicate one build to one aspect?
Perhaps I'd understand you'd use this for farming casual players in bg's, but then again I'd wonder, what for in the end?
Strictly speaking, double attack does not grant more damage per hit compared to buffing up other stats. Even accounting for stat drop-offs past 250 points, the best you're ever going to get out of double attack as a Psi is 40-50% chance, translating to a 20-25% direct boost to DPS over the long term. But that's ignoring the secondary effect of double attack, which is that you actually attacked twice. This means you can generate two stacks of Breakdown or Pyrolysis from a single attack, meaning you can be detonating max stacks more often. Double attacking also means you remove twice the stress you would have with that attack, so stress management essentially stops being a thing. You also don't have to waste GCDs on Phantom (assuming it triggers GCD) as often because you have a decent chance of having an extra one show up all on its own.
Double attacks can also crit, which I didn't figure into my original number. So assuming a 50% chance to crit and deal 1.65x damage (or a 30% crit damage bonus) and assuming a 40-50% chance to double attack, your DA will contribute a 33-41% increase in DPS over the long term, without accounting for any other benefits from the double attack. That kind of a multiplier is actually worth considering, given even primary offensive stats will eventually fade away in increasing benefit just because of how big the number gets. Funnily enough, this nerfs the Pally, Scout, and puts another nail in the Engineer's coffin as any class that doesn't have rubies for DA/Crit Chance/Crit Damage is automatically going to have a much harder time gaining this extra multiplier. But that's a topic for another time.
I'm also not sure why you're confused about the point of the guide. The build is dedicated to doing MAJOR damage. That is its sole concern, everything else in it is to extend survivability without impacting its ability to do all the damage. Doing damage isn't limited to either PvE or PvP, it functions in both settings. Now if you have a specific role to play that is NOT strictly about damage, such as applying debuffs or CCs, then yes this build is not for you. You can also make the argument that outside of Support/Suppression Aspect the Psi doesn't have the necessary bulk to survive if focused by more than one assailant. The counter-argument to that is... don't end up in that situation. As he said, in PvP the build is made for burst damage. You work the edges of a fight, find a guy that needs to die or is already being damaged, and you end his fun.
Clearly, in more organized PvP this probably isn't going to work unless you have some way of guaranteeing you get the support you need to survive. In random BGs or open world PvP, though, organized fighting is unlikely. And remember, you can always fade from a fight by using Twin. Regardless, though, the build was probably MOSTLY intended for PvE and is basically the most efficient PvE DPS build you can get for the Psi. There are so many DPS classes in the game that it's a waste to squander the debuff/CC potential of the Psi in something like Domi.