- You have the Leviathan part wrong. The Ascians gave the Sahagin priest the Echo, not Leviathan.
- Byregot is the god of craftsmanship, in fact. "The Builder". Every beast tribe has some pretty good skills at crafting things, from the Sahagin with their ballistas to the Ixalis and their hot air baloons :3
- Llymlaen being the goddess of navigation and sea explains itself easily => You need wind to sail.
- Louisoix didn't have the Echo, or at least he never used it. The kids in Ala Mhigo who wanted to summon Rhalgr didn't have it either, from all we know. Not only beastmen can summon, but anyone.
- I've never seen Kobolds having crop or growing anything :P

Finally, Shiva was an actual person, it seems, dating from the beginning of the Dragon war. At least, her myth started back then. The Twelve "exist" for much longer than that.