I made a post about this ~3 weeks ago, submitted a bug and posted on forums.
Skull is using the TBC change and it’s practically unusable atm.
EDIT: As of 15/10/2019 It seems that skull is fixed, currently after a few tests i’m getting random ticks ranging from 100-500 instead of the flat % every time!
EDIT 2: Okay so they fixed so it isn’t a flat percentage but it’s still not affected by armor reduction even though the flee is physical. Can provide screenshots of a warrior taking 500+ dmg in beserker stance but he has 42% damage reduction from plate set.