Dilan didn't know that Rory knew a lot more about his Undying Origin ability than the others. Their Soul connection was much stronger than he thought and it allowed even the subdued subject to understand and control bits of the master's power.
Dilan had known that Rory was given shreds of his Origin ability, which resulted in her receiving a super regeneration-like trait. But what he didn't know was that her super regeneration kept improving the stronger his Origin ability became.
He was also oblivious to the temporary enhancement she received whenever his True Undying Essence was activated.
That was also why he was not sure why Rory was suddenly of a different opinion than the others. At first, she seemed to speak in the other's favor. She agreed that it would be foolish for him to attempt killing the Sun God.