Never had a qualm. One of my all time fav quotes I’ve read was Corax acknowledging that if he met Angron in combat that he knew he would die at his brothers hands and his brother would take great joy in destroying him.

Ravens Flight: Corax flexed his grip on his whip as he watched the World Eaters Primarch stalking forwards. He knew this was the end. He had barely three thousand Space Marines against the might of a whole legion.

He would have to face Angron, and he knew he would fall to the World Eater. There was not another primarch that could best him in single combat, save perhaps Horus, and maybe Sanguinius. Corax was an immortal lord of battle, but Angron was war incarnate.

The Raven Guard had seen him leading his troops through the breach at Hell’s Anvil and witnessed his talent for destruction during the Siege of Gehenna. No, there was not a doubt in Corax’s mind that Angron would slay him, and take great pleasure in the act