Not even the green dragons entertained the thought that he was telling the truth...They knew prince Domino's personality fairly well, making them certain that he would have actually come all the way here to put Felix in his place than do such a crazy thing.
Another issue they found about his story was his strength.
Sure, he was strong enough to slay red dragons, but they knew that it would be impossible to repeat the same feat against royal dragons.
Don't even mention the elite royal dragons participating in the ceremony. Their foundational strength was simply a chasm that couldn't be crossed by Felix anytime soon.
As for his void domain and other killer moves?
They knew that all of his strategies were now in the open and had been studied by everyone interested in creating defensive measures or counter-attacks against them.
Hell, they doubted if he could even slay royal dragons at the radiant rank with the same abilities and strategies.