The reason for the conflict between the Xbr'aal and Mamool Ja in Yak T'el is not very sensible. We are told that the two were at war over access to fertile land to grow crops, but that is not something the Mamool Ja should require. Mamool Ja appear to be mostly carnivorous judging by their teeth and their agile hunter physique, i.e. they should not be eating plants, except the occasional taco shell (and it's not like you require taco shells to live). Mamool Ja should be hunters, eating meat from animals they catch, which are abundant in the jungle around Mamook. The Miqo'te U tribe live in much harsher conditions in Forgotten Springs at the edge of Sagolii desert, subsisting on hunting sandworms. Mamool Ja should have it easy in a jungle with abundant prey.
What would make perfect sense on the other hand, is if the conflict was over unspoiled hunting grounds. The soil being contaminated with aether naturally leads to said aether ending up accumulating in the bodies of animals that eat the abundant vegetation. The animals have evolved over thousands of years to tolerate it, but the Mamool Ja, who were only confined to the lowlands a few centuries ago, are suffering deleterious effects from eating them and want access to hunting grounds in the highlands. However, the Xbr'aal are using that land both for growing crops (they are omnivores after all) and hunting, so the highlands cannot sustain both populations at once. With this setup, Koana's solution is almost identical - he would ask his colleagues in Sharlayan to devise a way to prepare meat from the animals in the lowlands in a way that purifies the aether out of it, which would require more advanced technology than what Mamool Ja currently have access to. I think something like this can be easily implemented in the current version of the MSQ without changing the quests at all, except for editing the text. You could even have Koana or one of the Scions speculate that aether poisoning contributed to the mutation enabling two-headed "blessed siblings" to be born, making it even more similar to radiation contamination.
The solution in the current version also doesn't make much sense, because using standard farming practises over a few decades, you can develop strains of plants that tolerate a lot of different climates, and given the dense jungle, obviously plant life can adapt to the particular aether. Life, as they say, finds a way.
I really think that part of the story should be changed somewhat, to something which doesn't sound so illogical in-universe. I am not claiming my idea is the best, but it can be implemented without changing any of the quest design and fits the rest of established lore. In general it makes most sense for the conflict to be over hunting grounds and the resolution to be for a way for the Mamool Ja to safely hunt and eat the animals in the lowlands.