We still don't know how Karn survived the Lightmass Missile. He very well could've fled to the hollows or his mount could have blocked it, we don't know enough as to his survival and it would be a massive outlier anyway.
Also, disagree with the scaling chain. Skorge is able to be damaged enough by Marcus's melee that he was forced to flee, which never happens with RAAM. Additionally, RAAM took the same chainsaw that could damage Skorge, blocked it with his hand, crushed it, and threw it aside casually. If you think it was his armor that blocked it, blood was spurting from his hand (Pain Tolerance for RAAM is a thing in the Locust Revisions btw), meaning it had pierced his armor, and his own durability was able to stop it.
RAAM was never damaged by Zeta Squad (Barricks squad) either, he was damaged by them shooting down his personal Reaver, and a King Raven crashing down onto him, then exploding. Even then, he was still mostly fine, with only his leg trapped and some minor wounds.
As for Sraak, he was able to beat RAAM in combat, but barely, and RAAM credits the win to his armor, so it's up in the air as to who is actually stronger.
Either way though, Karn is at the bottom.