Rex needed time to think. He found the source of the amulet and … it was anti-climatic. In a good way. Not turning into a monster. Not going to lose his mind, being, or soul. Just a little bit of extra power and a piece of jewelry stuck to him. He met the creator face to face and was given freedom of choice. Do whatever or seek to persuade dragon-kind to abandon the prophecy.
He could just retire right now. Just go back home. Well, go back and serve the military and then eventually go back home. Stop risking his life day after day being a hazardous adventurer. Rex didn't join for fame or coin or noble purpose of saving the world. He just wanted to “fix” his problem. A problem that never really existed other than his head.
Fear. Fear of the unknown. Of the future. That's what a prophecy tries to address, really. To attempt to answer a question of something in the future. Evidence-wise, prophecies develop with none and tend to stay rigid even long after the originator died. Tradition and religion keeps it stuck, no matter the race. Even deities get stuck.
Rex understood the world in facts. Taking pieces of history and putting together a picture. How many 'prophecies' saved people destroyed in The Mourning? Could The Mourning been prevented if people challenged the various prophecies and made action with what they saw in front of them?
Perhaps Q'Rocknar thought of the same thing. Spoke out against the Dragon Prophecy and became an outcast. As powerful as dragons are, they still fall into the same trap as any other race in herd mentalities.
Rex needed resolve. Not hide. Not stay in fear. Fear would diametrically oppose any progress to challenge the prophecy.
Too many burning questions. The Dragon Prophecy isn't really a secret but what exactly it said should be researched. Maybe logic can reach a few more dragons. Or draw their ire and carbonize Rex...re...