About that arcanically-induced disease...I'm not sure that it was arcanic...since Achaxetanians couldn't use arcana. Something to be addressed elsewhere.
Anyways, the disease doesn't have any effect on the Kemite. The Archaxetanians withdrew from political contact with everybody when it happened, and the Kemite monarchs had a silent agreement with them anyways that didn't include much contact. It was a silent submission for the compensation of relative domestic autonomy.
As for the Fae, it doesn't say that they taught them how to wage war. It just says the Fae told the Kemite how to make weapons and what they were used for. Hence the undisciplined and untrained army. You don't have to be aggressive to know how to make a weapon. I doubt there are many blacksmiths who want to chop heads off.
