Ragnarok Yatagarasu is kind of a pushover. The low difficulty is probably an outlier in the grand scheme of events. e.g. Ragnarok Ixion, or the upcoming Ragnarok Vuithra. I think when Japan DMM first designed Ragnarok and the Core reward, they didn't have downstream usage for the core except for exchanging the Rare Grail. Later when SSR divine awakening arrives that tie in with the core exchangable for draconic eye shards, I think the advent Ragnarok will get harder and harder, just because the rewards have a greater usability.