Well, yes, I had noticed.
My point was that the Spirit Book must surely be more than the two chapters in the core Runequest book reiterated, together with a list of spirits from the Prosopaedia and their associated Rune Spells from the Red Book of Magic, as we already have all that in those books.
Shamanism and Spirit Cults is an area I would love to see developed, and I think needs development to work well at the table. As other threads are showing, people aren’t finding it easy to integrate shamans in to their games.