Micah Bell may have been Red Dead Redemption 2's chief antagonist, but Dutch didn't need his help to betray Arthur. The leader of the Van Der Linde gang spent the whole game becoming more treacherous and violent as time went on. Sadly, his ultimate betrayal of Arthur was not surprising in the least, and would've likely happened even without Micah's influence.
[Warning: The following article contains spoilers for RDR2.]
The dissolution of the Van Der Linde Gang is one of the main overarching plots of Red Dead Redemption 2, and a lot of that is fueled by the actions of Dutch himself. He proves himself to not be the wise and thoughtful leader that Arthur and the other gang members believed him to be, and his recklessness results in the gang's downfall. Dutch stayed loyal to Micah in RDR2, but the decisions that led the Van Der Lindes towards their downfall were made by him and him alone.
From the beginning of Red Dead Redemption 2, it's hinted that Dutch isn't as reasonable as Arthur believes him to be. Even early on, when Javier mentions that Dutch shot a girl during a robbery, it's clear that Dutch has an unnecessarily violent side that Arthur doesn't want to believe. This resurfaces later as the gang is dealing with Angelo Bronte, where Dutch viciously murders him before feeding his body to an alligator in a display of brutality that shocks those present. Dutch's willingness to dole out unnecessarily brutal deaths is a hint that he is not the honorable leader that Arthur once thought. RDR2 is not a story of Dutch's glory, but rather is an exploration of his faults and how they eventually ruined him. That included his penchant for violence.
Dutch Would Have Eventually Seen Arthur As A Threat In RDR2
Despite his constant adherence to his own plans throughout Red Dead Redemption 2, Dutch is quite inflexible once he sets his mind on something. He repeatedly tells Arthur and others that they have to stick to his plan in order to survive, even as circumstances continue to worsen around them. Dutch wants to be the one in charge no matter what, and he wants his orders to be the law of the gang. Dutch would never relinquish control to anyone for any reason. Even though RDR2's gang had several potential leaders, as far as Dutch was concerned, his plan was the Van Der Linde Gang's destiny, and he wouldn't let go of it no matter what.
The final reason Dutch's betrayal was entirely expected actually appears very early in Red Dead Redemption 2. In one of his early conversations with Arthur, Dutch randomly says that he expects Arthur to betray him someday. This is especially egregious considering that Arthur thinks so highly of Dutch and supported him until his decline became much more obvious later in the game. It really speaks to Dutch's paranoid nature if he is willing to believe that even one of his most loyal followers would be willing to betray him for no apparent reason. This is the biggest hint toward Dutch's fall to evil in RDR2, and proof that he didn't need Micah's intervention to turn on Arthur. If he believed that Arthur was after him, then he would betray him first.
Dutch is sadly nowhere near the man that Arthur thought he was. While Micah played a major role in bringing down the Van Der Lindes, Dutch was always going to turn on Arthur, and likely the rest of the gang eventually. Red Dead Redemption 2 is ultimately a tragedy, and Dutch's actions are the root of the gang's sad fate.