Why add it now? We can connect it to the impending arrival of RD, but it’s also possible they recognised something that might be useful for the playerbase - even if some don’t see it as helpful. I mean, CG doing things to help the playerbase might be a stretch, but it’s not something we can dismiss out of hand.
Re: farming DCs anyway, I’ve seen more than one of these debuff feats that wasn’t very compatible with the DC material node, so slow-farming the feat via that node was sometimes prohibitively time consuming, and I’m sure some players may have been unable to complete the feat using that node at all.
I’ve regularly used 20 Conquest energy to pick up all (or nearly all) of a debuff feat on an unsuccessful attempt. Disarm and O66 in recent Conquests, for example. I always found this preferable to playing several battles on manual getting 1 or 2 at a time.