Rapture world would hold great interest and great annoyance to the God-King. A version of Christianity did exist on Caspia in the distant past, and it along with every other faith, sect and religion was utterly eradicated to the point where even its name was forgotten by almost all of the world's peoples. Today, only a few scholars have even guessed a few facts about it. Caspian and his Great Ones, being immortal and having lived through its domination, of course remember everything about it and almost all have no love of it. Many would be eager to test Yahweh's claims of omnipotence and immortality, though.
Yahweh and Yeshua would be extremely confused by the existence of Caspian and the Great Ones: beings that they did not create nor have a hand in making. They would treat them as rival deities if their egos would allow for it. Swift action would be undertaken to restrain them and consign them to the Lake of Fire quickly, or strike them dead with holy lightning if that fails.
Caspian's opinion of Yahweh would be a comparison to a football player showing up to both impressve the cheerleaders and intimidate the competition. "The 'Lord' Yahweh is a macho boast. "Look at me! I am the great and terrible Lord!" A truly great person does not have to brag about it. True greatness dosen't need to draw attention to itself. A truly worthy god of the cosmos is concerned about the effects of their actions upon said cosmos, not about how they are perceived by underlings. Yahweh is not great. He is merely delusional and megalomanical."