Du You released the Heavenly Disaster Demonic Dogs without making a move himself, hiding in the dark. Even the curse of the Cursed Crow King was held back. After all, this was mainly a test.
It is well known that the power of the Giant Beasts has always dominated over various monsters. If calculated on a star-level basis, most Giant Beasts would be on par with those of 6 stars or above.
So, if the Heavenly Disaster Demonic Dogs could handle a level 10 Giant Beast with relative ease, it would mean that his current strength is already at the top tier within his class, even though he himself is only at level 7. As he advances, he believes that there will be few who can challenge him.
The reason Du You didn't claim to be invincible was self-knowledge. Others might not have as high a level or skills as him, but they might have various types of equipment and tools that he couldn't match.
