The challenge Rowan faced when it came to Boreas could be roughly summarized in these three sections, which were the Shell of the Divine Kingdom, the internals of the Divine Kingdom itself, and finally the Divine Spark. In order to kill Boreas without alerting any of the other gods, he would need to counter all the advantages the god's Divine Kingdom gave to them.
The key to the first problem would be Circe. Rowan knew that it would be nearly impossible for him to find the location of Boreas's Divine Kingdom in a stealthy manner.
It could be anywhere, not even necessarily on Trion, in a head-on battle, he would have only needed to kill Boreas a single time for him to trace the essence of the god when he resurrected inside his Divine Kingdom and use Astrolabe to deliver him into his stronghold, but Rowan would be using the ascension of Circe to bypass that first hurdle, the Shell.
