Imo, one in-between option is to add finisher moves that can't be buffed unless otherwise stated. Although when I was suggesting support job / skills in the past I suggested associating it to a max / casting player. For example Enfire enhances the next 5 weapon skills for 100 potency, or curse which increases enemy damage by 10% up to 1000 potency, or haste increases skill speed and spell speed by 100% up 800 TIME calculated potency and while Astrologian casts spells they add another 200 potency to the haste (time calculated means how much potency was gained by acceleration, because an 800 potency black mage spell is always 800 potency you didn't gain 800).