Thanks for the feedback folks.
My reasoning on the slayer promotions was that undead slaying already exists and was easy to acquire...and the scions don't seem any less viable because of it.

We are talking about wasting a promotion here...you are trading +20% against EVERYBODY for double that promo against a
much narrower subset. It is actually weaker than taking shock, for example.
I have to disagree here. If you're against ljosalfar or svartalfar, elf slaying would be FAR more powerful than taking cover or shock. Because it would affect ALL of your enemy's units rather than just a subset of them. granted, it won't work against other enemies, but That's hardly an issue, because with all the elf slaying you'll be doing, you'll rack up a ton of xp that can be spent on more general promotions.
and what are you gonna do with those units after the war with the calabim is over?
Personally? I'd delete them and make more. Playing as Sabathiel, it's quite easy to crank out new units at lv4, in one turn, in any major city. One recent bannor game, I put order temples, gallows, and command posts everywhere. Any city with a couple of hills could make a new lv4 champion in 1-2 turns. Which in most cases, was actually faster than transporting my existing army back from the frontline to wage war elsewhere.
Theocracy + crusade + military State + conquest
The above civic/building combination grants +80% military production, and 6 free xp for new units, as well as near zero maintenance for a colossal army. From there, you either get Form of the Titan, or run Apprenticeship instead of military state, to get the requisite 7.5 xp to make new units start at lv4. Then with the above system, you can crank out units with Combat I & II plus "x Slaying" of your choice.
My general point here, thoughm is that these promotions can't be countered. With shock, you can attack with archers, or horsemen. But when you're ljosalfar, you can't just not attack with elves. You don't HAVE any non elves. Unless you built the pact of the nilhorn.
Also, why does it make sense at all. What's so different about humans, elves, dwarves, lizards, orcs, that isn't simply covered in basic combat training. Sure elves have a dextrous, agile style. but so do human assasins. Dwarves may be a bit slow and clumsy, but so are bannor champions in their 15 foot thick armour.
Orc slaying for the chislev isn't too bad, because it's the only one they have. It makes them highly effective against one race naturally. But with this plan for the bannor, it will make them ridiculously effective against anything. like an overpowered swiss army knife.
Things like vampire slaying are logical. You carry crosses, garlic, wooden stakes, silver weapons, sun magic, etc. Specialised equipment for the job.
Personally, I'd say.
1. No orc/elf/dwarf/lizard slaying. Or anything else that targets the entire population of a civ.
2. Reduce the bonus of all other "x slaying" abilities to 30%