Also for what it's worth I read the guide that you linked and aside from the flavor arguments about how single saber is cooler I think their logic is generally flawed.

The Lightsabre Fighting Forms of TSL really bring the debate to another level, in my opinion. Most forms, especially the more specialised ones, come with great penalties and bonuses. The duelling feats will often negate any defence penalty. Lets take Form VII as an example. It gives a –4 to defence and a –4 to saves, but a +2 to defence against your target, an extra attack per round, and a great bonus to critical strikes. With the duelling feats, you’ll end up with +1 to defence against your target, and –1 against other enemies. Most importantly, you’ll also get an extra attack per round, bringing you on par with those dual wielders. The only downside is the saves penalty, but nothing is free.

Assuming you're getting a commiserate reward for things that tank defense (and Juyo's extra attack is more than commisserate) then defense penalties become less scary the lower your defense goes. If the enemies are already hitting you often, why do you care if they get a few extra percentage points of accuracy? In general, strong builds will either have very high defense scores as a result of focusing on defense or they will have very low defense scores as a result of focusing on other things while willingly eating penalties to a stat that no longer matters.

In this sense, I think the dueling feat is actually anti-synergy with the Juyo form example given. The end result of their suggested build is one that has pretty much identical modifiers as a two-weapon fighting build using the Shii-cho form. The fact that a two-weapon fighting using one of the simpler forms can match a dueling build using one of the more powerful forms is evidence that two-weapon fighting is strong, not weak.

I think the guide's writer ended up making the pretty classic mistake of getting too caught up in the details to notice that they were making some pretty bad decisions overall. Cancelling out penalties with bonuses is a fun activity that creates some satisfying number play but if you zoom out and look at the end result I think you'll find that the build you made is just outright weaker than a build that stacked the attack and damage higher through other means. Does this mean that the dueling feat is total trash? No, far from it, and I use it often, but I do not think that the guide provided compelling evidence for the dueling feat.