I will always stand by the fact that Kaito did the right thing at the end of the 5th Trial.
Shuichi's lie wouldn't just "have a low chance of succeeding", it wouldn't work at all. Monokuma was definitely monitoring Shuichi's every move, so he would have known if Shuichi had met Kokichi or disappeared from the cameras. Especially since the cameras literally everywhere. Literally.
Kaito did everything he could (and evеn more). He didn't "betray Kokichi", he didn't "abandon the plan at the last moment", he wasn't "forced to do something stupid for the sake of the plot". His decision was logical and justified. Shuichi would have just been digging his own and his friends' graves with that lie. Kaito realized that this was it, this was the end. The plan had completely failed and there was no way to save it. That's why he left Exisal.
It was a mistake on Shuichi's part to fully reveal and lay out the entire plan. By the time he realized that he should have played along and led everyone to a false verdict, it was already too late. There was nothing he could do.
But I'm not saying this to blame Shuichi for everything. His actions are understandable, his arc throughout the game was precisely that he learned to uncover the truth, despite all the obstacles. To reveal the killers, no matter how hard it was, no matter how much he didn't want to. Yes, he didn't realize in time that he needed to support the plan, but that was literally the opposite of what he had been learning all this time.
And another argument in Kaito's defense. He was running out of time. He had been holding on for the last few hours purely by the power of his stubbornness. However, he is not a superhuman and he cannot defeat his illness with sheer willpower. I think he felt that he had very little time left. And even if we assume that Shuichi's lie had a chance of success, it would most likely have led to long conversations, arguments and persuasion for another hour or two. And Kaito simply couldn't afford that luxury.
I feel a bit peeved every time Kaito is accused of "giving up" at the last moment. Even as a joke. Kaito did everything he could in that hopeless situation. This is the hill I will die on. Kaito did the right thing. He had no choice but to give up.