Collision boxes and hitboxes should be made separate

So currently, hitboxes are the same as collision boxes. Large cubes or rectangular prisms that somewhat match an entity's volume. The problem with this, is that:

• A: They don't rotate with the mob, making it awkward to hit large mobs like slimes 
• B: They have a lot of space outside of the model, or vice versa

Now currently, the boxy shape of hitboxes makes sense, it allows them to work as perfect collision boxes when interacting with blocks. This should not be changed, since doing so would either result in clipping through blocks, or a chance of being unable to rotate because of blocks.

The solution to this would be separating hitboxes from collision boxes. If done right, collision boxes could continue to serve their purpose of block interaction, and improved hitboxes would mean damage would be done much more accurately in regards to a mob's model.

Of course, it might seem like a lot to have to make new hitboxes for every mob in the game. But, in theory, the existing models could be used as the hitboxes, solving the problem of creating new ones. (Note: "In theory". I do not know if this could actually happen, but it seems plausible)