"Our lives are not our own. We are bound to others, past and present. And by each crime and every kindness, we birth our future." - Cloud Atlas, Sonmi-451
OK, I came up with an idea:
What if we transfer the potential and star force enhancements into regular stats and remove % potential and enhancements, and make the badge untradeable?
Let's say a character with 1000 INT from AP has a badge with potential + 10% INT x 2 so it makes + 200 additional INT (excluding equips). We make it a regular stat and the badge gives now +200 INT. When a character levels up, he no longer receives % bonus from the badge, and he can't transfer it to lower level characters on his account so that they can benefit from large stat boost.