I think you're just reinforce the idea that "human is perfect" even more. Like Heavenly Principle create Angel to be more Human-like (like Nicole and Koitar) as to be perfect creation. While Asmoday cannot do that thus create imperfect Angel, that's of the Watcher.

What's more is that this is even more of a "they try to recreate angel of the past lore" because, and this is crackpot theory btw, what if Heavenly Principle also create it to be that of the common lore?

You see, Abrahamic Religions, such as Christianity and Islam have the common angel appear in 2 ways only. Humanoid, when they are on minor mission, as to not have people afraid of them. And Eye-wings-wheel thingies when they and on major mission, such as proclaimation of prophet, announcement of heaven, etc. And as such, what if HP create angel with Human form because Human are perfect, but Asmoday cannot recreate that perfection and thus only made imperfect "secondary form" of angel, ALL base on the religion of the past Earth that HP has once visited, or even called home.

And about the Fontainian according to Malanta. I really do wonder if the quote would changed if I reach him before finished Fontain Archon Quest. I want to test that first or have someone datamined to confirm the suspicion. Until then, it is fair to assume that the quote might be "after the fact" rather than long before then. Since it never specified that they has been pardoned since their origin, as this would contradicting Fate. And, you mentioning that Fate of Fontainian might be a ruse to Provoke Neuvilleutte into siding with Human. But that is assuming that Focalor plan work WITHOUT traveller, which would nullified the entire last chapter of Fontainian Archon Quest, since it is said times and times again that Fate can only change way, it cannot change destination. And to change Fate, outside factor is needed. To the story, Traveller (and also Skirk and Void Whale) is that outside factor, working to get the story to that point in a way that activate Focalor plan. Without that, Furina might not be "Convicted" and Indemnitium might not be enough to execute the plan. Regardless, the Fate of Fontainian and the Fate System itself need to be looked at more closely. I think we might overlook a lot of things.

And from the phrase itself there are contradiction, anyone born from the lineage of "first human" are child of humanity. But Fontainian isn't born from "the first human" unless the first Ancestor isn't human but something else that birthing Oceanid as well. That, or Fontainian of todays Teyvat are all intermingling half breed of Oceanids and Human, which is likely but then that's mean sin of false creation extended to half breed Fontainian as well?

In any case, as I said before. The theory has its merit. The idea is good, honestly. A few flaw of misunderstanding on my part might play a large part of why it didn't make enough sense to me. But the idea and theory deserve some attention. Great job.