Personally i only have three achievements left to complete battlemaster, but im sure there are others out there who arent as lucky as i am to have been able to do them either with a 10/15 man from my server or from openraid.
My question is, now what? 5 manning most battlemaster achievements is quite impossible. Perfections, resilient victory, and others need a coordinated effort to obtain and 5 people wont cut it. I know that there have been times when some of those were obtained by luck (and in many cases, RBGs too...which is how i got a few)
I really disprove of blizzards decision, i'd love to finish Battlemaster and i probably will soon as my last three achievements are quite simple, just time consuming (To The Rescue! in AB, Persistent Defender, and Frenzied Defender in WSG)
I think it wasnt a good idea to make the only premade RAID groups available for RBGs.