I like to imagine the late game tedium of the game was intentional as a storytelling device. As the player gets more and more fed up with Dutch, the maim missions get more and more tedious. Thus, the game encourages the player to slow down a bit and interact with the game world. Be it side quests or just exploring, all of this helps with Arthur's character development as you see him helping more and more people and valuing things that aren't just the gang.