Ok I'll bite.
Again false. Far stronger? Please. He WAS strained, the reason he has a 'calm' face during this scene is to make it seem that he's not. It plays right into the whole 'psychological warfare/instill fear' thing he goes for.
I am stating facts of what was stated in the book, while you are assigning your own emotional assumptions. Corax had one lightning claw, his other hand had a lightning whip which was destroyed during the fight. Corax attempted to kill Lorgar with his remaining functioning hand which had a lightning claw, he was stopped by Curze who then defiantly lifted Corax's straining claw upward away from lorgar. Here is the exact quote from the book
"Corax looked to meet eyes as black as his, in a face as pale as his own. His claw strained against a mirroring weapon, both sets of blades scraping as they ground against each other. One claw seeking to fall and kill, the other unyielding in its rising defence. Where the Raven Guard Primarch’s features were fierce with effort, the other face wore a grin. It was a smile both taut and mirthless -- a dead man’s smile, once his lips surrendered to rigor mortis. It was the Night Haunter. Corax sought to wrench his claw free, but Curze’s second gauntlet closed on his brother’s wrist, so that Corax would be unable to fly away and escape his fate. Curze looked upon his prostrate brother and ordered him to rise from his knees, disgusted at his cowardice. Corax was not idle as this exchange took place. He fired his flight pack, burning his fuel reserves to escape Curze’s grip. The Raven Lord’s claw ripped free, and Corax soared skyward, carried on jet thrust away from Curze’s rising laughter. "
Again not true. He fled because he was heading to the areas of the battle which were most fierce (as stated by the enemy themselves) and to assist his men in escaping, he cared about keeping his legion alive.
From what was demonstrated in the book Curze was far stronger than Corax, Curze defiantly lifted Corax's straining claw that was striking downwards. Corax had the advantage of inertia and leverage, yet Curze still overpowered him without showing a single sign of strain. At that moment in time Corax was scared for his life, Curze could have killed Corax then and there. Corax had a single functioning hand, Curze had two functioning lightning claws. Curze trapped Corax and could have stabbed him at any moment, the only reason Corax escaped is because he burned out his jump pack to run away.
No, he hated himself for letting Curze's parlor tricks get under his skin and for not staying and denying the enemy two commanders.
Corax is a proud individual like most of the primarchs, and believed he was superior to most others. Corax had a wounded ego after his encounter with Curze, he ran for his life and he knew it. The very fact that Corax believed he could have stayed, killed both Curze and Lorgar in his condition was lunacy on his part. Corax was tired, injured, his breast plate had been shattered, and he only had one functioning hand/weapon.
Corax was assuaging his own wounded ego by telling himself he could have won if he tried, he was bandaging his wounded pride.
And yet he did just that.
Corax with his own strength, inertia, and power was unable to escape Curze's grasp. It states this in the book itself "Corax sought to wrench his claw free, but Curze’s second gauntlet closed on his brother’s wrist, so that Corax would be unable to fly away and escape his fate". The only reason Corax was able to escape was because he burned out the remaining fuel reserves of his jump pack in order to gain the necessary inertia to break free.
Corax required the external inertia, and power of his jump pack being burned out to escape Curze's one handed grasp upon him. That demonstrates how vastly stronger Curze was then Corax, in a comparison of strength.
He could have punched Curze in the face before he had a chance OR stopped his free claw with his other free hand(since only one was directed at Lorgar).
Did you even read the book? Corax's lightning whip was destroyed, his breast plate was shattered, and he had one functioning hand left, which was used to wield his lightning claw. Corax was unaware Curze was even there, and then Corax struck downward with all his strength to strike Lorgar dead.
Curze intercepted Corax's only functioning hand/lighting claw, Curze then grabbed Corax by the wrist and made sure he couldn't escape or maneuver. Corax was unable to do anything on his own, it was only by igniting his remaining fuel reserves that he was able to escape.
Corax had no free hand to punch curze in the face, he only had one functioning hand to begin with, and then curze grabbed Corax by the wrist with his free hand.
Much like Corax, please do assuage your ego since you clearly lost this battle.