You’re focusing too much on the word ‘mortal’. Non-demon unit.
Its just about unit variety, for me anyway. I don’t care if they’re human or beasts, I just wanted a new unit that wasn’t daemonettes, like every other god has got.
To me it simply boils down to this - Slaanesh has waited the longest for any kind of update, and got the least out of it. I waited patiently for Slaanesh because I thought it would be well worth the wait. And while what we got is awesome, there’s still not a core of the army that appeals to me, so yeah, I’m disappointed.