That's the message *List* view, not the message view.
I would like to add it to the message view's customizable bar of icons at the bottom of the message view (see images). That way, when I read the message I can immediately click to delete or hide it, move it to another folder, etc. Now, I need to close the message first, then select it, open the menu you showed, and click on hide. That's 4 clicks instead of one if I could put it as an icon in the customizable bar of the message view (which I prefer to the floating icon anyway).