There's actually a decent chance it is Ishikawa writing it, or at the very least being oversight on it; while she's the current main scenario writer, that doesn't mean she writes every individual patch chapter personally (as opposed to the broad strokes) -- nor does it mean she doesn't write other stuff. And she got her start in this game writing raid storylines, after all. (Coils and Omega are both her work.)
If not Ishikawa, honestly, I'd suspect Banri Oda writing or overseeing it. After all, he's the other lead writer, and one of the loremasters; Pandaemonium figures far more deeply into key MSQ-related lore than previous raid series generally have. (Plus, I think he's the one who wrote the Eden raid storyline, though I may be misremembering the Famitsu article I'm thinking of.)
