Contradiction with Genesis 1:21
Isaiah 51:9 speaks of the Lord's arm cutting Rahab and wounding the dragon, while Genesis 1:21 describes God creating sea creatures (which include dragons) as good creations, contradicting the idea of destruction.
Genesis 1:21: And God created great whales, and every living creature that moveth, which the waters brought forth abundantly, after their kind, and every winged fowl after his kind: and God saw that [it was] good.
Contradiction with Isaiah 27:1
Isaiah 51:9 refers to waking up to cut the dragon, while Isaiah 27:1 predicts the future punishing of the Leviathan, suggesting a different timing and nature of the act.
Isaiah 27:1: In that day the LORD with his sore and great and strong sword shall punish leviathan the piercing serpent, even leviathan that crooked serpent; and he shall slay the dragon that [is] in the sea. [piercing: or, crossing like a bar]
Contradiction with Job 26:12
Isaiah 51:9 shows the divine act of slaying the dragon as a past event, whereas Job 26:12 explains the sea being divided by God's power, which does not suggest defeat of a dragon.
Job 26:12: He divideth the sea with his power, and by his understanding he smiteth through the proud. [the proud: Heb. pride]
Contradiction with Revelation 12:9
Isaiah 51:9 mentions historical events of slaying a dragon in the past, while Revelation 12:9 refers to the dragon, the devil, being cast out in a future context.
Revelation 12:9: And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him.
Contradiction with Psalm 74:13
Isaiah 51:9 calls for God to awake and act powerfully, implying inaction; Psalm 74:13 reflects past power where God already broke the heads of dragons, highlighting past actions.
Psalm 74:13: Thou didst divide the sea by thy strength: thou brakest the heads of the dragons in the waters. [divide: Heb. break] [dragons: or, whales]