BOOKDRAGON

However, the problem with this is that Aaravos at least appears to go from powered/heart-ed version:

To de-powered, heart...less? version:

...when he's imprisoned. At least, according to the way Zubeia tells it.

Meanwhile, in Ripples, we see what is presumably Aaravos's actual "fall," as the "Fallen Star"—a literal descent from the heavens. This occurs long, long before the events of Aaravos's imprisonment, before dark magic, before Elarion.

I'll note that part of what I'm taking into account here is a note from the artbook on Aaravos's designs:

As a "fallen" Startouch elf, Aaravos can only access a fraction of his former power.

So it seems like the assumption to make would be that Aaravos lost his powers and status when he was cast from the heavens, which is also where I would assume Laurelion dies and Aaravos is "born" if the Laurelion/Aaravos as the same being dichotomy was in play. Then why is his heart not blackened until he's imprisoned?

One possibility is that his empowered appearance is an illusion he's maintaining—another manipulation, that's dropped when he's imprisoned.

Another possibility is this is all bullshit, and everything is as generally assumed before: when Aaravos was imprisoned, the majority of his power was somehow stripped.

Leaving that aside for a moment, let's take a look at the order of operations here, historically.

Humanity looks to the stars to save them, but the stars do not respond:

— Patience

At some point, humanity is granted some kind of blessing from the heavens, long before humans built cities and became powerful:

— Patience

ALSO at some point, humanity is granted the power of primal magic. By tradition this was from the unicorns, in particular Leola:

— Tales of Xadia

However, this magic is forbidden them:

— Ripples

Aaravos is cast from the heavens in a calamity that creates the Sea of the Castout—again, long before dark magic:

— Ripples

Further, in the retelling of this story, Aaravos notes that the stars apparently were satisfied with the results of casting him out. It scarred the land, and frightened the humans—and their claim on primal magic—into submission:

— Ripples

I'll add another note from the artbook here on Aaravos's design:

Some designs had a strong, authoritative vibe that suited other Startouch elves, but not our "fallen star."

Finally, let's look at this again:

Aaravos, obviously, on his knees and in despair. A feminine-appearing elf who is almost certainly another Startouch elf, by the horn shape and the design of the crown on her brow.

I've seen at least one person cast this as a rendition of Aaravos's punishment, in that she represents the other stars and gestures as if to say "behold how far our brother has fallen."

But y'all. Y'ALL. Please.

We have seen this gesture FAR too many times for it to be something else, at this point. This is mercy, and love, and the passing of a torch.

So, let me clean this up into what I think happened:

The stars are largely absent gods, indifferent to the fate of humans and interested in only their design/prophecy of the world.

Leola, another Startouch elf (or else we're gonna stretch the definition of "unicorn" pretty far), takes pity on humanity and grants them the secret of primal magic.

Leola is somehow punished for this transgression. If Laurelion is Leola, she is killed. (The Celestial elves, in this case, are the guardians of the stars' order and power in Xadia. They are the last line of defense against this sort of thing.)

Aaravos, who loved Leola, either speaks on her behalf or otherwise rebels against the order of the stars. Aaravos is cast out. If Laurelion is Aaravos, he is robbed of his heart and his power.

"Leola's Last Wish" is to continue to be a guide to humanity, through the darkness.

Aaravos, meanwhile, fucking loses his mind and decides to burn down everything. He will destroy everything the stars put in place in all of Xadia, and he will leverage humans to do it.

Aaravos begins to spin up dark magic, and when the time is right, gifts it to humanity as the inciting action of his plan to tear all of Xadia apart. More on that here.

ADDENDUM: Chatting with @raayllum immediately after writing this and they raised the possibility of Leola being Aaravos’s mother, given the parallel to Sarai in the statue, and YES that makes so much sense. Particularly regarding the star-child constellation, him adopting her crown, and why he might be punished along with her. I like this explanation better than them being lovers, even if it means TDP gains yet another goddamn martyr mother.

Anyway, that's it! Mystery of Aaravos solved.