Higher piercing stat decreases armor break damage bonus.
This behaviour is independent from character(at least for Cerebella and Ms. Fortune) and game mode (at least in training and story mode).
Example:
Setup: 2 Cerebellas with 959 atk (no atk bonuses from moves). First one has piercing stat = 15% and second one has piercing stat = 0%.
Charged attack in both setups deals 720 damage. But after applying armor break (via battle butt) charged attack in first setup does 840, second 860.
Device: Huawei Honor 10
OS: Android 10
This behaviour is independent from character(at least for Cerebella and Ms. Fortune) and game mode (at least in training and story mode).
Example:
Setup: 2 Cerebellas with 959 atk (no atk bonuses from moves). First one has piercing stat = 15% and second one has piercing stat = 0%.
Charged attack in both setups deals 720 damage. But after applying armor break (via battle butt) charged attack in first setup does 840, second 860.
Device: Huawei Honor 10
OS: Android 10