You've still yet to prove how they are worse. That is because you can't. Let's talk objectively:
-Dante Exum has never posted a positive VORP for a season (this season, VORP is -0.2). Both Udoh (a pure reserve) and Sefolosha (a 30-something player coming off of a significant knee injury) are posting a positive VORP (0.3 and 0.2, respectively).
-Dante Exum has never posted a positive BPM (+/-) for a season (this season, BPM is -3.1). Both Udoh and Sefolosha are posting a positive BPM (3.3 and 0.4, respectively).
-Exum has an inferior WS per 48 (a paltry .087) to both Sefolosha (.115 which is better by ~40%) and Udoh (.197, more than double).
-Exum has a 12.6 PER which hardly more productive than Sefolosha (who's contribution and role isn't at all conducive to PER) at 12.1, and is dwarfed by Udoh's 17.5 (again, whose role isn't to be productive).
-Neither Udoh or Sefolosha are on guaranteed contracts heading into the big cap space year (the only time salary matters for basketball purposes is in the context of being under the cap or above the luxury tax, a situation the Jazz haven't really been in since while Sefolosha and Udoh have been on the team).
My point isn't how great Sefolosha and Udoh are, my point is that even compared to end-of-bench players, Dante Exum is substantially and demonstrably worse at winning games. This isn't even actually my point; it's in response to your completely baseless claim that Exum is 'objectively' better than either player, which makes your claim that Exum is worth twice the salary (actually a lot more than that) almost-hilariously ****ing off.
We don't have to be flagrantly intellectually dishonest about this. Exum isn't good and he's being paid insane money on a longterm deal considering the reality of the situation.
I'm of course going to hope that he learns how to shoot, have good posture, breathe properly, and not shatter with nearly-impressive regularity. Nobody is actually rooting against Exum.