When we think about the spread of the Lunar Way, we can break it into two waves.
The first is in the Heartland of Peloria, where it took at least a full wane before the Lunar Way was truly entrenched. Even 375 years later, initiation into Lunar cults is followed by a plurality of the total population. This despite New Pelorian – the language of Lunar rituals and discussion – being the lingua franca, and the native myth structure being the most compatible with the Lunar Way, and a long tradition of Nysaloreanism. We can include the West Reaches in this, and many mysteries of the Red Goddess tie into some of the old mysteries here.
Interestingly, the Pentans seemed to be able to incorporate the Moon Goddess into their existing Sky pantheon. The Char-un and even Sheng Seleris seemed to have little difficulty accommodating the Red Goddess into their myth structure.
So with this first group, the missionary Seven Mothers cults were ultimately quite successful at first getting the Red Goddess incorporated and acknowledged into the existing myth structure (the Battle of Castle Blue was likely key to this), and then slowly bringing people into less superficial understanding of the Lunar Way. Still after 375 years, most people in the Pelorian Heartlands have only a superficial embrace of the Red Goddess and her mysteries.
However, the second was far less successful. With the Orlanthi, the Lunar Way hit a wall. To start with, the language was unrelated. And Nysaloreanism didn’t even make that much headway during the Broken Council era (unlike the Darktongue influenced Arkatism). To make matters worse, the primary god was actively opposed to the Seven Mothers and an enemy of the Red Goddess.
In Sylila and the Lunar Provinces, old Dara Happan colonies were most receptive to Seven Mothers missionaries. Lunar colonies like Furthest were established with settlers from the Heartlands. These were already Lunars, and not later converts. But in none of the Lunar provinces do Lunar cultists make up much more than a third of the population – Tarsh has the highest percentage, but that’s primarily settlers from the Heartlands, not converts.
In Sartar, the Lunars really didn’t make much headway at all. The occupation was too short for much conversion. Even with missionaries, it takes a long time to make much headway, especially where the local religious traditions resist accommodating or incorporating the new religion.
If we look at the historical Islamic conquests we get a similar slow rate. For example, a hundred years after the Islamic conquest, Persia was only about 7% Muslim, and it took another hundred years for Islam to become the majority religion. . Conversions in the first 20 years post-conquest were generally slow, as Islamization was a gradual process driven by social, economic, and political incentives rather than mass forced conversions. Across non-Semitic speaking regions, ~5–10% of the population typically converted to Islam within 20 years of conquest.
Same thing with Christianity in the Roman Empire. It took a LONG time to make much progress with the gentiles. Maybe 10-20% of the Roman Empire was Christian some 250 years after Paul had his moment along the road to Damascus. The empire became majority Christian around 400 AD, with maybe 3-4% growth per decade. Now that is with a heck of a lot more sticks and carrots, using existing networks of power that had been in place since the conquests of the Republic.
You can see the same slow progress in Anglo-Saxon history. From Augustine’s mission (597 CE) to widespread Christian dominance (c. 700–750 CE), the process took roughly 100–150 years for the Anglo-Saxons to become majority Christian. Ireland likely took more than 40 years to become majority Christian. Probably took a good century or more as well. And both were in a very different environment than trying to persuade the people of Dragon Pass not to worship the main storm god who lives in Dragon Pass (and whom they get direct tangible benefits such as Rune magic from).
I think the Lunars can be forgiven for not doing any better with a newly conquered land with its own vibrant religious traditions.
Another way of looking at this is that the Seven Mothers missionaries in Peloria made it easy for the Red Goddess and her pantheon to be accepted among her fellow Sky gods. Sure she had to fight like hell at Castle Blue to get there, but after that there was an entry. The Seven Mothers could prepare the way for the deeper Lunar mysteries, and it all fit pretty easily.
That didn’t work with the Storm Gods. They had only a peripheral involvement at Castle Blue, likely as Carmanian allies, and the Red Goddess’ victory there meant little to them. Orlanth and Storm Bull were simply irreconcilable with the Red Goddess’s association with Chaos. And where Orlanth was present, Humakt went with his brother. And although Ernalda and the other Lightbringers might accept her presence, Orlanth would not. And Orlanth is just to central to the Orlanthi religion to be easily marginalised. In Saird, the Lunars could just settle colonies and found (or at least expand) cities with Lunars from the Heartlands – that really wasn’t practical in Sartar or Prax (despite the efforts of Sor-eel with the Borderlands). Maybe if the Lunar Occupation lasted a century we might have seen something, but twenty years was just not enough.
I thought in Castle Blue was Compromise Gods VS Red Goddess to prove herself. That is certainly what some have asserted it to mean. But the Compromise is the Compromise. Castle Blue was not the Cosmic Compromise and does not add to or detract from it.
The more interesting thing to me is Yelmalio’s stubborn defiance. Although he is Neutral towards the Red Emperor and the Seven Mothers, he’s downright Hostile towards the Red Goddess. He might accept the empire as a good mercenary, but he’s not accepting of the core Lunar Way itself.