That makes sense, but I still don't see why it's a requirement. If you have it, use it. If you dont, use the best you have. I have both black spindle and eirene from the gunsmith but I tend to use eirene much more. No one in the raid had a problem with my using eirene and we downed every encounter up to the sisters in one try. The raid leader, who was skeptical at first because we were entry level light and complete raid noobs finally told us he would raid with us over some of his regular group any day. If you have a solid team who listens, coordinates, and communicates well, you can do the raid and maybe even "easily". My friend stayed on and beat Oryx after I left to get the achievement. He said it was about the same as the first half of the raid in terms of difficulty. Honestly, I found the hardest part up to the daughters to be the freaking bunny hopping across the bells, the ships, and the catwalks.