Mercenary Storymode?

I thought the Mercenary single player mode as previewed in the places I saw it talked about, was supposed to be more like a “Slay the Spire” type mode where you go down different potential paths of building your deck rather than another “Book of Heroes” rehash. Am I mistaken or thinking of something else or a different upcoming mode here? I was kinda disappointed by the Mercenary single-player campaign.

The Book of Mercenaries is not the Mercenaries mode expected to be released later this year. Just confusing because of the similar name