I look at it this way.
Chaos primarch suck so hard that abbadon is the current chaos champion.
Abbadon only finally had a successful crusade by losing a fucking blackstone fortress.
He is a huge fuck-up... and some how the chaos primarchs are WORSE.
Even fucking Typhus thinks mortarion is a little bitch... and calls him out too his fucking face... and morty does NOTHING.