Psalm 93 was written as a direct counter to the Ugaritic myth where Anat (female deity) helps Baal, after he is injured by gods of the ocean, death and momsters of the sea (in Ugaritic these are called Yan, Mot and Lotan... in Hebrew they are Yan, Mot and Leviathan). With Anat's help, Baal recovers and becomes king.
Unlike saying Baal reigns after a battle, the reign of God is not recent, it is from of old, and it will not change. Baal whose reign may be preempted by another encounter, not God, though. This psalm says God is master over the waters and over creation and over everything. He will not be dethrowned and has always been reigning on His throne.
[Unit 5, BE 109, Transcript, 30-