why a chaos lord, why not a sorcerer lord with MoT, Third Eye and conjoined homunculus, and skull of katam with power familiar. You get +6 to cast with up to +3 more each turn, you get lore of tzeentch and whatever else his slann has, which if he is smart would be lore of life, in which case your set. Also if he has lots of stegadons, why not take any hard hitting units like dragon ogers? They cost 20 points more than your ogers and do way more damage, today they took out 8 cold one knights in one round of combat and then 10 temple guard in the following 2.
Scyla Anfigrim? I dont think he is worth it really, I would instead try to free some points and get a big creature yourself like a shaggot to easily take out his steggies.
Also rather than armour of morselieb, why not take an enchanted shield and amulet of preservation on your tzeentch lord/hero thats a 2+/3++ against magic too, I have one on a disc and he hasnt died once yet.
When life gives you lemons..... BLOOD FOR THE BLOOD GOD!