Resource pack makers cannot create overrides for the appearance of armor while the player is wearing it, only of the "item" as it is held in the hand/shown in the inventory

What I expected to happen was...:
I would expect there to be some kind of assets/models/armor folder with relevant jsons for implementing overrides for armors.

What actually happened was...:
No such folder exists; the only way to edit armor appearance is by editing the relevant textures, so I cannot, as an example, create a helmet that appears as "horns" and still grants all the benefits of armor. Currently custom models of this kind are only available by editing a carved_pumpkin, which provides no armor benefits, and instead acts as a carved pumpkin.