For those interested in reading some of the pages of the Rubicon, the raid lorebook, here is a link! https://imgur.com/gallery/rubicon-lore-books-2-5-d2ZBFls
One of these stories is an interesting look into the history of the Witness by one of its Dissenters, a historian. Little is told to us about the foe, not their nature and capabilities, other than their resolution to prevent the Witnesses goals. They drove them right to the edge-- drawing a comparison to a Hive God being held at knife edge within their Throne World!
And then this foe tried to offer the Witness and alternative, a choice. You can imagine how that went.
It's very interesting that this matches the shape of the Gardener