Um... why fix it? It's neat, realistic, and contributes to the fun of the game.
I'm almost 100% sure that the regions around Terran have enjoyed migration from our regions. Thysan in particular comes to mind. Maeotis before D'Hara retook it was growing way too fast for it to be endogenous growth. When Asylon took Shoka, it already had over 1,000 peasants, despite being often attacked and pillaged by monsters.
And are you sure migration doesn't bring religion with it? Because there's no way Triunist temples are causing 99% conversion rates across 5-6 regions of low population full of monsters and undead. Plus, I noticed rogue rurals seem to grow quickly in population until they equal the population of their neighbors, then they slow down.
What he means by "fix" is make is so that when peasants migrate, they take their own religion with them.
As for the rogue rurals, I think that they benefit from a military force that prevents the monsters from invading from quite as many directions.
