So my theory is that the HK organised religion believed that it was the One God organised religion and that all One God worshippers are part of it when it practice, the One God worshippers in Ymaryn are members of Mylathadysm as a cult/sect due to the Syncretic value of Mylathadysm. Because of this, it was a case of an organised religion lacking control over its followers, but it was one organised religion failing to convert/command the followers of a second organised religion. While they may consider themselves to the One God organised religion, in practice, the HK organised religion is that, the organised religion of the Highlanders. Despite what the HK priest may claim, their domain isn't that of all One God followers, but just HK One God followers. So it wasn't a case of our One God followers jumping ship, but rather it is the opposite with our Mylathadysm followers refusing to jump ship to the HK organised religion.