Isn't it interesting how the atonement narrative has developed over the expansion? Comparing it to the previous expac, I don't particularly recall reading any dps-focused posts regarding atonement until late in Cataclysm. If memory serves it was around the time more guilds started to work on H Ultraxion and then later on the tendon burn for H Spine.
It was in t14 where posts started to appear here and on the battle.net forums where you had people emphasizing the importance of strictly healing via atonement and acting as the half healer, only doing "real" healing before or during peak raid damage of an encounter. As far as I am aware those posts came primarily from 10 man raiders. Raiding in 25 I was still very much of the mentality that I would only use atonement while building evangelism stacks for AA. I think you would also be hard pressed to find any 25 man disc priest doing much anything back then but spirit shell and PoH spam rotation.
All of that changed however when they removed auto-aegis from PoH. We didn't have much choice but to focus more on atonement with a ridiculously buffed HPS from penance they gave in compensation. Sometimes I seriously wonder what they were thinking with that given the large amount of tweets from Ghostcrawler regarding how they want to also encourage us to use penance as a directly heal. Particularly in contrast to the initial posts from him on the Beta forums around a year ago, we received such a large reaction to the QQ regarding 1 penance = 3 evangelism stack changing our rotation that they reverted it within a week. I was shocked by how recklessly they were making and undoing changes with what seemed only player feedback.
Anyway, I think this has got to be the first time in MoP that I have heard a 10 man disc priest arguing for stacking spirit. I'm not agreeing or disagreeing with your points, just commenting on how inconsistent it is with the rest of what I have been reading the last year.