Isekai protagonists from science-worlds likewise know what happens when planets fail to be born.  You end up with asteroids.  They aren't especially poisonous.

Then there's the notion that Acavna waited around in place near the missile collision site, or missile exit site, to be hit by fragments large enough or fast enough to kill a goddess, which She didn't see coming and dodge.  Again as science protagonists know, when you are dealing with moving moons around, and distances on the scale of planets, it is really hard for anything to hit anything by accident.

Possibly there was an original missile approaching at near-lightspeed; and when it collided with the moon, that sprayed up so many massive fragments that 0.01% of them hitting Golarion would still have ended life on the surface...

But that doesn't square with Amaznen needing to sacrifice Himself to neutralize magic on those fragments.  If secondary ejecta had been the primary threat to Golarion, they'd have been an unmagical threat.

You'd furthermore think that the alghollthus, if they were able to steer such a hypothetical hyperkinetic missile at all, would have known a missile at that energy would utterly destroy Golarion's crust including themselves if not intercepted.

Also if the alghollthu magic upon the fragments was potent enough to lay Golarion waste in its own right, apart from the fragments' kinetic energy, and required Amaznen's self-sacrifice to neutralize - then why should the alghollthus not lay that lethal magic directly about Azlant?  Why put it on a distant incoming asteroid first?

And furthermore - though this is not a physicalist area of expertise, it comes up if you just visualize out events and think about them - supposedly Acavna's divinity stuck to those fragments that killed Her, one of which was the Starstone, which then reached Golarion and became individually able to create gods on the order of Aroden.

Aroden was the strongest of mortal-ascended gods.  Hitting Acavna should not create thousands of fragments all of which could then create Arodens.

Arguendo:  Possibly all of Acavna's divinity stuck to the Starstone and not to any other fragments that killed Her?  Maybe it was that exact fragment that struck the final blow?

Counterarguendo:  Maybe, but then that's another weight of burdensome improbability required to make the whole story work.  One also notes, as an isekai protagonist reading through other stories of gods' deaths, that it is not usually said that the weapon that kills them retains their divinity.

Also also, if either of Amaznen or Acavna did willingly sacrifice themselves to meliorate the blow - why did They do that?  To briefly extend the lives of those mortals living upon one planet, until they came to Pharasma slightly later?  It's a strange trade for an ancient god to make, and Amaznen and Acavna are said to have been Lawful Neutral and Chaotic Neutral respectively; neither Good.

...Anything else?

Oh, all kinds of things, if dath ilan were to list out everything unusual whether or not the improbability is obviously relevant.  For example, it's said that Iomedae's helmet melted during Her ascension but remained intact enough to become a major artifact, the Thorncrown of Iomedae.  There's no artifacts like that said to be tied to Nethys's or Irori's ascension.  This doesn't obviously tie into any other anomalies, and doesn't seem intuitively shocking given the basic premise that the Starstone ascends things that get physically close to it, and dath ilan is not actually going anywhere with this observation; but if you're trying to actually think about a puzzle you will write everything like this down in one place.  If dath ilan forced itself to make up a guess about this random possibly anomalous fact - something something Starstone treats divinity in a way that makes spatial proximity matter to an unusual degree?

Any real scientific puzzle will contain a large number of extra pieces - and in advance of the solution, you don't know which pieces are extra.

So what does dath ilan think actually happened?

Lacking direct observation, you would probably have too many hypotheses and too little evidence to narrow them down.

You might speculate that the currently-known Starstone was the whole original 'poisonous remnant' rather than just a fragment.  If there were fragments, they might have been from pieces of moon, blown outward along a similar trajectory after the original Starstone blasted straight through the moon at high velocity.

You could theorize that the Starstone was aimed from the beginning to pierce through Golarion's moon toward Golarion - rather than Acavna moving the moon into place, and in futile error - and that the Starstone killed Acavna through Her connection to that moon.  Possibly Amaznen tried to save His sister-deity and the Starstone sucked the power out of Him and killed Him too.

This hardly seems certain.

Yes yes, it's admitted speculation; but it's often wise to start by trying to develop any consistent speculative model at all, if you're trained and confident in your own ability to throw out any pieces or wholes in which you later spot a problem.

Mmhm.  Well, keep speculating, then.

Maybe the alghollthus tried to catalyze the Starstone's 'poison' with their magic rather than having the power to create a weapon like that from scratch.

Or maybe, the alghollthus had nothing to do with the entire matter and were only blamed afterwards.

...Or maybe it wasn't the whole alghollthu civilization, but a particular band of alghollthu mages influenced by Rovagug, like how Rovagug is said to have infected a Sarenrite city built far above the Dead Vault.

Why blame Rovagug?

Abadar was taken by surprise at how the Age of Darkness ended Zon-Kuthon's exile, so some prophecy-breaking force was involved at some point.  And if Amaznen and Acavna did willingly sacrifice themselves, maybe it wasn't to save mortal lives; maybe it had more to do with Golarion being Rovagug's cage.

That in turn suggests that an unmeliorated Starstone strike would have benefited Rovagug, or that the gods feared it would.  Maybe the missile was 'accidentally' aimed at the Dead Vault?

...But the main point is just that the thing that is written in most books, can't possibly be the true story; and that's obvious as soon as you try to visualize the process step-by-step.

And you might also suspect, if what was written in books seemed obviously wrong, that there was some reason the real answer was hidden - though the general state of disrepair in Golarion epistemology, from the standpoint of the isekaied physicalist, is such that even this guess is very tentative!  The myth-composers could just be that invalid.  But still, you'll go looking for truths that are not only overlooked but concealed within the Starstone, faced with a story like that.

It begins in the City of Lost Omens, with a casting of the spell Mage's Decree, by which a wizard can make themselves heard for miles around, all through a city...

"This is Ione Sala, oracle of Nethys, apprentice to Nefreti Clepati.  Stand by for extremely urgent instructions in three hours; prepare to convey or translate those immediately."

A lot of predictable ruckus follows!  Those who didn't understand the original words (in the language there named Taldan, called also Common in Absalom) shout for translations.  People who've lived their life well enough to stay ignorant of wild rumors are even more confused, and inquire after context.

Many wise and proactive people will panic early, to avoid any later rush; and start heading away from the Starstone, since earlier rumor held that's where shit would go down.

Certain others, however -

“- that’s illegal, eighty thousand pounds in fines, she can bargain it down if she talks to the Primarch,” says Cassdra Eliomole instantly. The nice thing about violations of this specific city statute is that you can’t really contest that they happened. (Guilty parties can of course teleport out, but it’s the rare high-level wizard who will accept being permanently blacklisted from Absalom’s shops and libraries and mage academies.)

The nice thing about this specific violation is that the wizard even named themselves, unless they are naming their ex-girlfriend to get her in trouble, which is the sort of thing wizards frequently come up with, thinking themselves cleverer than they are.

  “- do you suppose it’s true, though,” says Mesich Aspexxon, her secretary, who has cooperatively gotten out the paperwork to be delivered to Sala issuing the fine and explaining how she can contest it, and is now filling it out with today’s date, the time, the investigating authority, the statute violated, and the source of the information by which Sala was identified as a suspect (“testimony to all Absalom”).

“Don’t be ridiculous.”

  “I mean, there’s the prophecy, right, and Ione Sala’s that Chelish Nethysian. She might know if the prophecy’s true, and the city to be devoured.”

“You can’t trust a Chelish person, and you can’t trust a Nethysian,” says Cassdra, with absolute surety. “So any sound a Chelish Nethyisan makes is just so much wind whistling through the streets, and we’re going to fine her for it.”

  “Well at minimum,” says Mesich, “I think we’ve got to think of who’s delivering the notice, you know, if she’s in a fighting mood, considering that you can’t trust Chelish Nethysians.”

…that is a complication. Cassdra bites the end of her pen.

The Office of The Public Interest, which handles the frequent and often impressive misconduct gotten up to by the high-level adventurers of Absalom – anything not appropriately handled by the city watch and the option of dumping some idiot in the drunk tank or the gaol – is the province of the First Spell Lord of Absalom, who is responsible for regulating the Arcanamirium and ultimately all spells cast within the city.  However, the position of First Spell Lord is currently held by Lord Gyr, of House Gixx, the Primarch of Absalom, who's not in fact a caster, but assigned himself that position anyways.  He's not in Absalom right this second.

The next most obvious person to storm in, given the implied threat to Absalom, is the Second Spell Lord charged with Absalom's magical defense:  Lady Darchana, of House Madinani, who also happens to be archdean of the Arcanamirium (though at seventh-circle she's not actually the most powerful arcanist there).  But Lady Darchana has long been on fragile terms with Primarch Gyr, both as his obvious rival for the true mastery of Absalom, and also about the snub of her not being named First Spell Lord.

    Mesich finishes the paperwork. “- Darchana?” he asks quietly.

“No, we can’t,” says Cassdra. “Gyr will rightly consider that entirely inappropriate - and think, she might declare that this represents a real threat to the city, which she of course will vanquish in his absence -”

      “Then you’ve got to contact him!”

“I am doing that!” Cassdra is applying his seal to her incident report at this very moment. Gyr resents, and is usually shielded against, Sendings, but he has some astoundingly fast carrier pigeons. He’ll hear of the problem in plenty of time.

—----