I have recently had issues with fighting mobs in my world, because often I will click places where I see the mob's model, but where there is no hitbox. The most egregious of these is the phantom, but it happens to an extent with all mobs.
Seeing as mob hitboxes are basically just cubes, and mob models are also cubes, would it be possible to make it so that hitboxes and models match up? If it's not, at the very least, hitboxes could adjust more dynamically like in the games mentioned in this 2017 article from Black Shell Media.
Relates to MC-197028. Perhaps Mojang will rewrite their entity hitbox code at some stage. Presently, all entities are confined to cuboid hitboxes. Introducing rotation and other adjustments to hitboxes would increase programming complexity.