Kind of a dumb question

This might be a dumb question but how is rarity actually applied? Rarity doesn't appear in the character stats section but instead the "On Kill Effects" section of your skills. You would think it should just be a global stat on your character that goes up with how much you juice rarity on gear, tablets, and waystones. If it's just invisible and still global, then why not just put it in the miscellaneous section of the character page?

And what happens with mechanics where you don't kill an enemy with a skill? Damaging ailments like ignite or poison, shrine effect, beira's anguish, and others where a specific skill didn't actually kill an enemy. Does rarity still apply in those cases or not?