I haven't fully read these exchanges, but here is some very brief input.
My take on HP is that the issues arise (for those that they do arise; eg not me) because they are both an (1) abstraction and also a (2) synthesis of interrelated systems (as in musculoskeletal, circulatory, and endocrine) combined with downstream interactions (how does neurological state a lead to morale b after events x, y, z?).
In a lot of D&D, the mechanic of HP is expected to do the heavy lifting for all of this (not even Dungeon World does this; disabilities does the heavy lifting for acute conditions).