The thing is that the sacrifice reward on its own after 1-2* characters is indeed mostly useless (though you can still get a rare soul by chance even at tier 1 sacrifice) but each and every soul sacrificed contributes to the vortex meter (the purple circle in the middle of the altar). The vortex has the ultimate rewards as it chooses (I think 5 or 6) items from the narrowest pool, which is G/A soul, Skill Shard and Legendary Soul (note: ultimate sacrifice and vortex rewards share the same pool, but vortex higher number of item given to you).
Yes, it does take an immense amount of useless souls to fill the vortex, but as each soul's essence worth is put to the vortex meter, on the long run you are better off killing them instead of selling.
Enti-2694
ok you need 500-1000 souls to win the vortex and you must use 500-1000 another souls to have the same? if yes it's not a good feature
It take me several month to have 1000 normal souls
I play all troopers all days.