https://serenesforest.net/three-houses/classes/class-change/
Stat Boosts from Class-Changing
Credits: DeathChaos
There are two types of stat boosts when changing class. Firstly, if any of the character’s current stats are lower than their new class’s base stats, their stats will be increased to match the base stats.
Secondly, every class has a unique set of stat boosts. These can be hard to notice at first, especially for lower tier classes. So long as the character is in that class, they will benefit from those stat boosts.