You're still assuming that Ardyn's interpretation of the facts is the valid one when there's no good reason to do this.
All we really know is this: 1) There was a plague caused by plasmodium parasites. 2) Ardyn decided, seemingly on his own volition, to try to cure the plague by absorbing it into his own body. 3) Because Ardyn turned himself into a walking, talking infestation, the Crystal considered him unworthy to ascend to the throne and chose his brother as king in his place. 4) Ardyn's brother attempted to have him executed, but it didn't work. 5) Ardyn grew incredibly bitter. 6) Ardyn's brother apparently still desires Ardyn's redemption.
There's no reason whatsoever to believe that the Astrals' reaction to Ardyn's being a walking, talking infestation was in any way unjust. Ardyn made a bad choice and had to deal with the consequences. Their treatment of Noct, meanwhile, appeared to be based on practicalities -- they needed a King who was powerful enough to defeat Ardyn, and nothing short of Noct's sacrifice would be sufficient. This is one of the most significant problems with the existence of a canonical workaround, for the record -- it completely destroys the context that allowed the original ending to be anything other than an unnecessary tragedy.
Since when was FFXV ever about "the gods and the crystal screwing people over by forcing things upon them?" That might be true of FFXIII and FNC, but OG FFXV clearly broke from that mold and was far more interested in inevitability than divine capriciousness.
It's also important to understand that there's a difference between archetypes -- the sympathetic villain, the hero sacrificing himself willingly, people conforming to divine will, a truly corrupt villain who brought about his own ruin -- and a cliche like the hero who overthrows the gods through sheer force of will. Archetypes might be staples, but their perseverance is largely a consequence of their lasting relevance. The attraction to heroes who successfully cheat fate by laying waste to the metaphysical foundations of their universe, in contrast, is a particularly modern pathology (I blame Nietzsche), and one that FFXV was much stronger for resisting.
Well, you don't have to reward the heroes for fighting fate in order to use their fight against fate to answer questions that went unanswered in the original game. If the point was simply to answer more questions, the best way to do that is the troll solution I suggested before -- have the alternate ending result in unmitigated failure, much like Ardyn and Ravus' attempts to find an alternate solution in the original game.
...on a more positive note, this is a brilliant detail. <3