The main plot point of the story can seem a bit odd, given that Linkara has arguably been through a lot of terrible things up until that point, and that he frankly managed to power his way through despite all of that with his usually swaggering egotism. However, it makes more sense when you take into consideration the most important events that occurred recently and how that would lead up to that point in the beginning of the film:
1) Linkara was forced to confront the fact that his arrogance and cruel egomania was making him go down the path of evil. In all prior cases, he was able to brush off the experiences he went through because he had always been able to fall back on his ego and successes to compensate for his trauma. However, finding out that he was turning into a monstrous person, and with hard evidence in the form of Holokara likely would have badly shaken his fortitude and self-perception. This probably wasn't helped that not too long afterwards...
2) Linkara ended up playing part in a huge mistake that caused someone else to be hurt, but he couldn't just undo the damage this time. When he fought against the likes of Vyce (twice) and the Entity, he made errors in judgment that caused harm to those around him, or made his problems worse due to his arrogance. The difference is that those lessons didn't stick because he was able to correct the problem before the lesson sunk in, thus making him grow worse and worse without learning anything of value. In the 6th Storyline up until the Movie however, he ended up fucking up multiple times without being able to properly resolve the situation, such as trapping Jaeris in his dimension due to his anger getting the better of him. This would have likely stuck with him, especially so soon after his journey to restore his magic, because Jaeris is a point blank failure on his part, and he can't just undo the mess he made instantaneously; he has to do it the hard way. This would have punctured his already shattered ego even further, probably bringing into question just how invincible he really was.
3) The next few villains after put him in positions of helplessness that he could not resolve at all without outside help. Prior successes against Mechakara, Insano, Vyce and the Entity could be considered pure luck or contrivances, but was internalized by Linkara as being purely his own power and success. But when Vyce took over Nimue, he was basically powerless to stop him until Jaeris intervened, and he was able to get NIMUE to full strength and had her defeat Vyce that time. The King of Worms was even worse, because NONE of his preparations worked against him, and he only won by accident. That realization of just how lucky he really was, how much his grandiose fantasies of superiority were just a lie built on sheer dumb luck, would have only destroyed his sense of invincibility, and made him more susceptible to finally falling into his depression/traumatized state.
