The Devourers did have a tragic relationship with their primarch, because Angron hated nearly everything about his bodyguards. His hatred of their role is understandable, because the existence of his bodyguards implied that he needed them; but when you're a bloodthirsty superhuman warrior, you don't need to rely on bodyguards to be with you at every frontline battle. The Devourers basically lied to themselves that their primarch didn't ignore them, which he did when the Butcher's Nails affected his sanity. They also couldn't keep up with him either, due to their bulky Terminator armor, not even in the heat of battle. It's also sad because at first, it was an honor amongst the World Eaters to be a member of the Devourers; but by the time of the outbreak of the Horus Heresy, it was seen as a dishonorable dead end in the career of a World Eater Legionary.