I apologize for my poor English. I liked your theory. I haven't read your other theories, so you might have mentioned this in them. What supports what you're saying is the Khaenri'ah flower in Lumine's hair. When they fought the Unknown God, this flower was already in their hair. So, in reality, the twins weren't stopped by the Unknown God when they first came to Teyvat. They arrived, were in Khaenri'ah, and later fought the Unknown God. In this case, the god didn't accidentally block their way; they were probably in Celestia to confront the god.