Adamai's FUCKING problem. Is that his only social contact for the first 13 years of his life was an old dragon who was all about recovering the lost Eliatrope glory.
Adamai was raised to be the Responsible One (iirc one of the webtoons comfirm that his life with Grougal was mostly training with very little affection or play.) He was raised for the explicit purpose of discovering what happened to the eliatropes, and, hopefully, bring them back. He's the last of their people!! He HAS to get shit right!!! And he was raised by a dragon, one of the oldest and most knowledgeable beings in the world!! Innit cool?
Well, in practice, that means Adamai has HUGE problems admitting he doesn't know something, admitting that he could be wrong, or overall listening to people. Because he should know better. That's his culture!! He was raised to be the best!! Everyone else is a fucking idiot about this. Adamai was raised by a dragon and he IS a dragon and he knows everything and really everyone else speaking up about eliatrope topics is a bitch who doesn't know their place. What do they know, anyway??
(What they know is that eliatropes do not exist in a vacuum, and bringing them back is going to lead to MANY sociopolitical changes. And also that the dofus + eliacube are huge sources of power, which, you guessed it! Can also lead to diplomatic incidents. Unfortunately, Adamai was raised by One Guy while completely cut off from the rest of the world, and so he seems to genuinely struggle to understand the concept of "even if you are morally in the right you might wanna chill if powerful people disagree with you.")
Speaking of isolation, you know what else was Adamai raised on? The idea that he has an eliatrope brother, who is his other half, his platonic soulmate, the one person he is literally psychically linked to. Which, good on him! But also, the way he behaves strikes me as... almost dependant on Yugo. Adamai only if ever hangs out with Yugo. His deepest relationship is with Yugo. He seems to be on good terms with other people, but considering we never see him actually like, have a conversation with them, I think I can safely say it's mostly a "friend of a friend" or "coworker" type relationship. So, yeah, no fucking wonder he takes it badly when Yugo rejects him in the OAVs. It's not about the dofus or who was right or wrong. It's about how Yugo is everything to him... and to Yugo, he's only one of many friends. Yugo is part of this world. Adamai isn't.
SO yeah, the combo of isolation + steel-solid belief that he knows best about eliatropes and dragons means that Adamai grows up to be kind of a bitch (said with affection) and it makes him especially suceptible to literally anyone willing to validate his beliefs, which is why he is voted "most likely guy to fall into a cult" two seasons in a row.