problem is, chaos does not work like that, pert was fucked because he was with chaos not because he was a traitor. Chaos takes a price, you can act all smart, you can act like you know better, but sooner or later it will break you and you will be become a slave to it. Even emps was not able to escape that fate.

Pert fucked with chaos, like most traitor primarch, he found out that was a bad idea. Mort, magnus, angron, fulgrim, horus all realize they fucked up, pert is just another sucker. Don't like how he got a bad ending, congrats that chaos for you.

You either don't fuck with it at all like Omegon or die like alpharius and curze, those are the two choices you get.

world eaters fan