Where in-game is this info from? We know what Voidsent are and they don't just crop up where-ever Darkness is strong. They are specifically summoned from the Shard that was Flooded with Darkness. And Voidsent were corrupted by the Darkness and are really just the corrupted life from the 13th Shard. Any time we see someone "turning" into a Voidsent in-game, a Voidsent from the Void is possessing their corpse. Sometimes the person's soul is still in there, most of the time it isn't.
Like it or not, the Eden Raid calls Eden the First Sin Eater and says it's the origin of all the Sin Eaters. This is a bit of a problem when you have what looks like things that originated from Eden existing before Eden ever sent the Flood of Light off.So a completely valid explanation is Amdapor seen random sin eaters, maybe not from the first, maybe just in magic hammer space, and they copied it. I would assume getting something to become completely aspected to one aether is particularly hard, especially given cross contamination is possible. Maybe they didn't have the means to infuse something with pure light aether and instead chose to imbue a preformed block and statues with light aether to mimic it as best as they could.
Sin Eaters are no more a natural thing then Voidsent are. Everyone in the 1st Shard will turn into a Sin Eater due to the Flood of Light infecting all of them with "seeds" of light which is exactly how Voidsent were created in the 13th Shard when it Flooded with Darkness. Being transformed into a Sin Eater doesn't speed up unless a person get really close to one of the high rank sin ethers though. Tesleen's transformation is show as being rather typical of how Voidsent "speed up" Sin Eater creation if Holmister Switch is anything to go by.I say sin eaters are a natural thing as the little boy in Amh Araeng in the Inn at Journey's End is slowly turning into a sin eater, it was not a forceful encounter. His aether was locked so only light could enter and everything else slowly seeps away or is being converted. Once anyone passes a thresh hold they are transformed into a sin eater. Normal people just wandering about don't chance because they can still regulate their aethers normally.
Allag did create artificial Voidsent... by cloning real Voidsent they summoned from the Void. They never actually "made" new original concept Voidsent. If Amdapoor were to be doing something similar, they would have to get a Sin Eater from a non-existant Flooded World of Light and then somehow copy that. The Source has never been so elementally tipped towards Astral or Umbral as the Void or the 1st Shard have gotten. So I highly doubt finding such a strong influence of Dark or Light on the Source would be possible.
I'm just saying... when the only source of a phenomena is someone Flooding a Shard with Light or Dark... none of that is how a world "normally" works. And in-game citations for a lot of these sin eater claim would be appreciated.