In my defense, I wrote it at work (don't tell the boss!), so don't have access to any sourcebooks. I had forgotten Valamin even existed, let alone any details about him. Given this, then the heresies may not make as much sense. Maybe the heresies don't acknowledge the existence of Valamin? After all, if the sect is making up new stuff, they are as likely to also ignore existing stories. And I like the idea of beliefs contradicting each other, so support of Larani and punishment of Valamin is no problem to me. Messy religion is the norm, and more fun anyway.
Maybe Valamin is really Larani's son, and she wanted to leave him behind and forget about that sordid incident back in high school?
Personally, I do not see Agrik raping or lying with Peoni - that's just how the priests explain it to the masses. The lesser gods sometimes created entities to aid them. In whatever way this happens, the two could have created Larani, Valamin, or any other figure. Whether it was a cooperative venture, or one was coercing the other to help really doesn't matter in the long run. After a time, the new entity may gain power, by whatever ways this could happen. If it was created by two deities working together, rather than one alone, then there is an excuse for it to have greater potential. Gods in my pHarn do gain and lose power over time, and so having one major deity be the product of two others is quite reasonable. If this power fluctuation does not happen in a pHarn, then these heresies make much less sense there.
So, for me, Larani could have started out as a powerful demi-goddess, gradually gained power and followers of her own, and only became a goddess of war well after becoming independent of both Agrik and Peoni. This gradual increase in power is key for me, because it explains why her church came into being well after the others. Valamin is still thought by some to be Peoni's son, but he is a minor demi-god at best. Because of his actions, he cannot stay with Peoni, so is sent to live with Larani. "You always wanted to be just like her - you just as well go live there"! "Hey sis - Mom kicked me out. You got a couch I can crash on till she settles down?"
As for more information about the battle between Agrik and Larani, I agree with you. But, I also think each major deity deserves a large writeup detailing their history through time, their relationships with the other deities, the differences in what the churches teach vs. what really happened, and a selection of known heresies. Assuming these heresies are believed, then the battle and its aftermath are much more interesting, and just waiting for someone to detail it. I always thought that Larani was just badly injured, not slain, though that may be from my not having read that passage in years. Shouldn't make much difference in the long run, either way.