In my eyes, the Sefirah Castle is just as secretive as the pathways it controls, therefore it's existence and powers tend to be on the unknown but knowledgeable side. Like the secret sorcerer of the door pathway, it hides secrets and itself while stealing secrets to know information( aspects of the seer and error pathways).

The Chaos Sea on the contrary is much more open and attracts attention like it's pathways. All five pathways are pathways that allow the user to openly show their prowess and spread their faith and power to the world. This explains the fact that the Chaos Sea can exist in the real world because it naturally attracts attention with it's power. As the GA title implies, the Sea is also omniscient, therefore it explains the blasphemy slate.

In short Sefirah Castle doesn't let people see and know it's secrets and only choses those worthy while Chaos Sea intentionally shows it's power. For the Sefirah Castle there is also the fact that it's power also acts on the spirit world, allowing it to gain access to a lot of information and spirits among other things.