To wage war against the Bohao cultists, who have essentially taken control of both worlds, you need to think strategically. Eliminating the leadership seems logical, but with no access to the central region where the cult's leaders hide, that's a dead end. Hunting down individual cultists would take centuries, and they'd just recruit more in the meantime. So what do we do? The best approach would be to cut off all supply lines of the ancient substance they rely on and destroy every concentration camp where they keep the unfortunates they intend to sacrifice on their altar. This should force the cult's leadership to come out of their strongholds and into the outlying tiers--which is exactly what the Seekers are after. The more enemies they attract, the richer the rewards from their downfall!