As you can see, i maxed Brienne but her abilities are not maxed. If I feed her more Heroes, nothing happens.
It’s the same chance to increase whether maxxed or not. Specials can still be raisex
Until the Special is maxed (8/8), you can still feed heroes to your chosen hero card to level that special.
Try to use same colored cards, 2* cards etc to raise the Special Level Up Chance %.