There are three problems I can see with your interpretation of the "aether cycle".
First: there's nothing implying that "physical aether" does not go back to the lifestream, in that scenario. Dead bodies are eventually destroyed (either by decomposition or other means), so once that happens, the aether that was in that body should go back to the Lifestream too. It's just not an immediate process.
Second: it is never specified that the aether is divided 50/50 between soul and body. Maybe the ratio is 99/1. Or 999/1. We don't really know, and dividing it on a 50/50 ratio is just arbitrary. So it is very possible that whatever aether goes into forming a body is meaningless compared to the aether needed for a soul. This could mean that the aether is eventually recovered, or that maybe it doesn't really leave the system since, again, bodies decompose and whatever matter was in them is absorbed by the enviorement.
Third: Maybe the aether needed for making a normal soul/body isn't significant at all in the grand scheme of things. Maybe the aether "lost" by the death of normal living creatures is like a natural evaporation on a pool of water. You might be losing water, but it's so slow and minimal that it doesn't really matter.
Primals, on the other hand, consume large ammounts of aether to manifest. So a primal summoning isn't like evaporation: it's someone with a bucket stealing the pool's water and dumping it into a lava pit. It might take him a long, long time to deplete the water, but it will happen much faster than if you let the pool be and evaporate on its own.
First: there's nothing implying that "physical aether" does not go back to the lifestream, in that scenario. Dead bodies are eventually destroyed (either by decomposition or other means), so once that happens, the aether that was in that body should go back to the Lifestream too. It's just not an immediate process.
Second: it is never specified that the aether is divided 50/50 between soul and body. Maybe the ratio is 99/1. Or 999/1. We don't really know, and dividing it on a 50/50 ratio is just arbitrary. So it is very possible that whatever aether goes into forming a body is meaningless compared to the aether needed for a soul. This could mean that the aether is eventually recovered, or that maybe it doesn't really leave the system since, again, bodies decompose and whatever matter was in them is absorbed by the enviorement.
Third: Maybe the aether needed for making a normal soul/body isn't significant at all in the grand scheme of things. Maybe the aether "lost" by the death of normal living creatures is like a natural evaporation on a pool of water. You might be losing water, but it's so slow and minimal that it doesn't really matter.
Primals, on the other hand, consume large ammounts of aether to manifest. So a primal summoning isn't like evaporation: it's someone with a bucket stealing the pool's water and dumping it into a lava pit. It might take him a long, long time to deplete the water, but it will happen much faster than if you let the pool be and evaporate on its own.
