Thats a big problem with AoS and reasons why probably some of the armies fall short in popularity.
An example:
As for dwarf Slayers. Them being quite awesome and interesting is showed off on their "bleak and standard" background of "standard" dwarfs (heavily armored, slow and purposeful defensive guys).
It's like with cooking. Everyone loves the cake's crumble, but if you are being served only crumble, after few bites it's really not that good as an actual cake with crumble. Different things make of good meal/cake and quite often those things are very different from each other (fat, salt, acid, temperature etc.). You cannot give someone a kilogram of lard and hope he enjoys is only becouse he previously said he likes to eat doughnuts* .....
*true doughnuts are boiled in lard.