Removing it from AROP? Sounds like a bad idea.
Wouldn't it be easier to make the (new) Drain strike quest for DS9 require level 95, as well as the presence of DS8? Leave DS8 as part of AROP. It would basically require AROP to be completed before the DS9 could be done. But I don't see that as a bad thing in any event, since they are the high end versions anyway.
If you remove this from Arop, which currently grants 1 reward per rift guardian kill, will there be any rewards for the rift guardian kills anymore?
Currently:
Mind Guardian - Dragon Fear
Bones Guardian - Spiked Scales 8
Heart Guardian - Primal Rebirth
Blood Guardian - Drain Strike 8
Or removing it from just the Blood Guardian?