Something doesn't add up regarding the connection between Amdapor and Norvrandt...

[geekgirl101]

Sin Eaters somehow existed on the First when the Flood of Light began, but declined to show themselves to the general populace for some reason. And at that time, the passage of time on the First was effectively a time stop while thousands of years passed on the Source. (This contradicts out-of-game lore interviews given prior to Shadowbringers, ie that a "proper" Flood of Light is just blank nothingness, but those could always have been retconned.)

Since sin eaters remain present where there is a strong Light source being emitted from a Lightwarden then there must be a point somewhere where there's a strong primordial Light presence for them to congregate, like a Bermuda Triangle where Light is at its strongest, and are unable to move beyond that point unless Light becomes more dominant on the rest of the star. This could explain why they weren't seen before by the inhabitants on the First. Emet-Selch summoned one to alter Vauthry before he was born so they must already exist somewhere. Like some have stated it's probably then a natural occurrence where overwhelming primordial Light aether warps living beings into Lightwardens and sin eaters. I think Thancred said something along those lines too when he ventured into the empty that if we remained in it for too long then the overwhelming Light aether would eventually turn us into a sin eater.

[TankHunter678]

Since sin eaters remain present where there is a strong Light source being emitted from a Lightwarden then there must be a point somewhere where there's a strong primordial Light presence for them to congregate, like a Bermuda Triangle where Light is at its strongest, and are unable to move beyond that point unless Light becomes more dominant on the rest of the star. This could explain why they weren't seen before by the inhabitants on the First. Emet-Selch summoned one to alter Vauthry before he was born so they must already exist somewhere. Like some have stated it's probably then a natural occurrence where overwhelming primordial Light aether warps living beings into Lightwardens and sin eaters. I think Thancred said something along those lines too when he ventured into the empty that if we remained in it for too long then the overwhelming Light aether would eventually turn us into a sin eater.

And given that Eden, a massive source of primordial Light, had been sleeping on the First then Sin Eaters would be able to form in its immediate vicinity, but until the light grew strong enough to reach across the world then the Sin Eaters would not be able to leave the isolated location that Eden was sleeping in.

[Ouen]

... at any point in time an Ascian could have setup a vision for one of the Amdapori to let them peer through the barrier and see these Sin Eaters. The goal obviously being to give the Amdapori a means to take the fight to Mhachi and their voidsent. With open war being possible it sets the stage for the War of the Mages and the calamity it sparked to follow.

I considered that Ascians might have had a hand in the matter, but it's hard to draw further conclusions until we know precisely what capabilities Amdapor had so I didn't explore that idea very much. However, reading your reply, a question that now occurred to me is why would they use Sin Eaters in particular? How would this empower Amdapor and facilitate more chaos than if the Ascians had not intervened? What did Amdapor and the Ascians stand to gain from this transaction that they would not have otherwise?

What benefits does simply shaping the golems into the aesthetic form of a Sin Eater confer? Wouldn't normal stone golems (e.g., the Clay Effigies, Mana Idols, and Mana Pots encountered while descending into the Crystallum) suffice? They already had normal golems that were very capable of fighting, why would they need to create additional golems that were doubtless more difficult to make than Idols or Clay Beasts?

A possibility might be that much like the patterns that arcanists and geomancers utilize or the way that various weapons have divots and carvings, certain patterns enhance the flow of aether. Taking the form of Sin Eaters might allow for stronger golems. However, I find this a weak justification for all the effort it would take for the ascians to step in and teach the Amdapori about cross-dimensional beings just to make their golems, already functional, more effective.

On a side note, something curious to me is that none of the "Gargoyle" statues in Amdapor Keep are identical to the gargoyle-type Sin Eaters (Tesleen's model). In fact, they are actually quite different if you examine them. Here's an album I put together comparing some of them.

If those were indeed made in the image of the Sin Eaters, then they're not 1:1 like the Winged Lion or Kuribu recreations. They are golems, but interestingly they are identical to voidsent, and NOT to Sin Eaters. This may be an oversight, as they probably didn't have models of the First gargoyle things made yet.

Also, this probably has no significance, but I found it interesting that the zombified Amdapori White Mages you fight are named "Amdapori Gargoyles" while the adds that look like what we think of as gargoyles are called "Putto."

[geekgirl101]

On a side note, something curious to me is that none of the "Gargoyle" statues in Amdapor Keep are identical to the gargoyle-type Sin Eaters (Tesleen's model). In fact, they are actually quite different if you examine them. Here's an album I put together comparing some of them.

Tesleen's transformation was different from the other sin eaters, that may have been down to her being instantly transformed by a more powerful sin eater rather than the lesser ones that take days to slowly transform.