Every episode discussion removal for spoilers that should be in the Source Corner has been incorrect for years. Nothing in the rules differentiates between episode discussion posts, rewatch posts, and a source corner. An auto-mod sticky comment isn't the subreddit's rules page.

Beyond that, the currently applied stance is dumb for season finales. Anime-only people for series with middling support end with series questions often enough that discussion threads have top-level comments inquiring what happens (or what was skipped for rushed season finales) that can't be answered other than redirecting to the non-rules source corner removing spoiler-tagged answers to their questions without redirecting them to the non-rules source corner.