Opportunity In Disguise! (1)
The mana core was different from the soul.
It was quite important, no, very important and essential, but at the end of the day, it had the tendency to grow rigid and basic from the most mundane of uses.
In fact, for most humans and beasts, their cores were formed naturally, having basic traits that usually involved the same general formation of mana and the function of storing said energy crudely.
Such a start was already non-indicative of a powerhouse in the realm of combat.
Mages and skilled fighters from powerful Families and Houses were groomed from their cores, avoiding this basic setup of the core that would eventually stick with time, becoming difficult to change.
Once a specialised flow and formation was created, specific techniques could be used along with more advanced applications of mana.