Concerning lower ability in a pillar, I think it's important that the lower ability is of the "lesser effect" kind, not the "much less chance of any success" kind. With a simple succeed-or-fail sort of check, reducing success chances can soon feel like the player is wasting his time even trying, and encourages the player to just dump all ability in the area to gain extra power in another pillar. After all once they have discounted a particular pillar so e.g. have halved their chances of success, its a lesser sacrifice to dump it completely, and from an action economy point of view better not to waste time on foregone conclusions(e.g. 75% chance of failure), and gain ability at your preferred activity.