This OP and title are a bit misleading.
The old grind isn't
actually returning, it's just being used as a mechanic in the battleground.
The more people you kill, the higher your rank will get, as you climb up the old pvp tiers. The higher the title of the person you kill, the more points they are worth to your team.
These will be cleared at the end of each battle, because they are a mechanic of the battleground not a persistent achievement.
https://twitter.com/holinka/status/497072524211912704
https://twitter.com/holinka/status/497083703680458752