I feel like that's a pretty well thought out theoretical! Will admit to still not having seen the new Dune movie so mostly going by the book.
I don't know if I explicitly ever read into Dune that particular "Dark Side" interpretation of the Duel before as since it is so solidly from Paul's perspective it seemed to be painted in terms of something nessisary to survive further and thus more like a morally neutral painted thing. A loss of innocence for sure but not nessisarily any more so than other fantasy protagonist who took the same sort of step of killing for the first time. He wasn't granted much autonomy to completely peaceful exit the situation by Jamis so his options were more or less try and kill or cement his one likely route to survival. With the "locking in fate" thing painting his choice to die in the duel rather than kill as maybe for the greater good for nebulous wibbly wobbly timey wimey reasons.
It almost felt to me since the books were so bloody weird with plot points shooting the moon (though after awhile more like jumping the shark in personal opinion) and the factor of such grand prescience weakened a lot of the moral picture of any grand themes of Paul becoming an absolute monster as he's got such a solid "greater good" he's working towards that doesn't really have theoreticals?
Like okay, Paul sees literally everything that will happen from the arrayed options so his demise is always placed as being stopping a series of dominoes from falling by plucking the first one to fall out of the lineup... but those grand losses are almost always impersonal. He at the same time is a human with human desires for personal safety for him and his loved ones which doesn't place him as nessisarily "bad" just kind of instinctively alive. The plot always frames this as ultimately selfish but really only from the perspective of having a complete and total knowledge of how everything single action is going to eventually play out. It's eclipsing human moral frameworks by this bizzare aspect of sizing it up to a Godlike scale. Paul can make a "good choice" as essentially a God working on that scale of knowledge or a "bad choice" as singular human with a bias towards survival. While an interesting hypothetical I think that removes him strictly from the territory as being at all relatable on a moral scale to a conventional ethical paradigm. Like for all Paul's prescience he is limited in his ability to affect the board state so a lot of what happens is painted as his fault because of a choice he makes but if you look at the choices made where he really sort of fucks the dog on a God-like scale it's generally for reasons which make him relatable as a person.
Absolute power corrupting absolutely or later themes that people really need to not think too collectively and not create cults stikes me as not being Paul's downside. He didn't ask for the power he has to be dropped into his lap and can never fully get ahead of the consequences of having that power so I don't think Paul is painted as being a complete subversion of being a self insert turned bad guy so much as being a " tragic hero Chosen One" just being a hell on earth situation that he needs to weather with highs and personal lows. The framing sort of struck me as a fairly typical compounding trauma storyline where all the terrible things that happen to him make him more "heroic".
This is all sort of personal opinion though. I feel like I don't exactly love the Dune universe. My reading of them was largely because while I was staying in Japanese guesthouses I tended to read whatever English novels were left behind by previous occupants.