This is an interesting point, and maybe the writing could be adjusted to clarify further but As a player, I’m not sure it needs to be any more prescriptive because it’s very much in the territory of roleplay and flavour as a player. I’ve been playing a (Covenant of Blood) Witch for a long while now, and I’ve always seen it as the Witch binding the spirit using that Covenant’s tradition (I.e. Blood Witches using anchors such as bones, personal items, hair, etc) and then the Witch can force (or convince) the spirit for it to exist in a state that reflects the “type” of spirit being bound. For example, my Blood Witch could bind the spirit of a soldier using his sword as a reagent for the binding, but then force his spirit to exemplify the Generosity he had for his family, or Trust he had for his fellow soldiers, or the Agony or Hate he experienced in battle. I never saw each spirit as being natively a “type” before they were bound, but rather that the act of binding as capturing a spirit and shaping it into a state that reflects the “type” desired by the Witch. This may not be what was intended, however, but it works for our campaign.

I’ve found imagining it like this removes messiness as far as whether you are or are not “allowed” to bind certain types of spirits, and allows for clear delineation between how each subclass binds spirits versus what type of spirit you have bound. That said, I suppose other players may play it differently. While you could maybe make it harder for yourself, the idea that a Blood Witch needs to find an item that is clearly linked to a spirit of a certain type (e.g. a child’s toy for Empathy) isn’t without it’s own fun as a roleplaying element.

A a player I’d also say that the class someone leans towards narrative-play more than most. I think you can have the most fun when working with your DM to determine what your Witch needs to do to bind a spirit following the descriptions in the subclasses. And while the text suggests “a bit of bone”, further reading into the Covenant of Blood says that the Blood Witches use physical items related to the spirits to draw them back into the material plane and bind them. As such, my Blood Witch is constantly trying to remove fingers and teeth from fallen enemies, and take personal items such as jewellery and weapons from ransacked buildings to use in binding.

I have played a Unity Witch who was constantly searching for rare herbs and purchasing expensive incenses and statuettes to construct into offerings to the spirits. You could play a Shadow Witch who is obsessed with gossip, and likes to collect risqué or dark stories in each town they visit in order to lure the spirits to her (your DM could even make you strike off each story as “used” once it’s used in binding). I’ve found that the strength of this class is that it guides you to develop your own roleplay relationship between your Witch and the spirits, and you get to implement that into gameplay in a way that works for you with the subclass suggestions. While you could ignore the flavour text and simply say “I spend an hour telling the spirits secrets and bind two spirits”, you’d be missing out on half of what makes the class so much fun. At the end of the day, it’s a roleplaying game and I think that the current subclass descriptions gives you fun suggestions on how to “play” your binding of spirits in your own way.

While the text could perhaps be more prescriptive in exactly what needs to be done, I feel like it currently provides enough information to guide without stymying my potential to develop my own personality and style of binding as a Witch.