You are absolutely correct. It's not only evident in Bloodborne, but it's a very good example of an under researched UI. The problems people have with e.g. equipping weapons when starting the game is a one clear problem. Mixing settings icons with item slots is a no-no, because the user expect the icons to be related to options. The inventory not allowing you to equip is contrary to logic. If there is an item, why not equip it from USE menu item. There has to be good affordance, a cause and effect approach. There are tooltips, but some icons are missing for the user to know what they mean and some are hidden.
We all have existing knowledge base created from past experiences, which affects how we approach any new device or UI. We usually expect things to work a certain way which changes from person to person. Some Souls players might expect some features based on those games from Bloodborne, but new players have no idea of their existence. But, even when use metaphor is previously learned, it doesn't make the design choices good. Evident in Bloodborne.
Still, best game whatever the UI usability is.
