Jut FYI John's path is completely different from this you will find out more about how his core's work much later in the future.
Now the ranking system for martial artists would look like this:
"Black Core": This rank represents someone who has just started to develop their mana core, and has yet to unlock its potential. Their core is heavily impure and often filled with negative energy.
"Red Core": This rank represents someone who has started to develop and shape their mana core. They have begun to control and harness its power. Their core burns with intense passion and energy.
"Orange Core": This rank represents someone who has reached a basic level of proficiency in the art of martial arts. Are considered the average, not particularly strong or weak.
"Yellow Core": This rank represents someone who has honed their skills to a high level of mastery. They have a deep understanding of the techniques and principles and are highly proficient in them.
"Green Core": This rank represents someone who has reached the peak of martial arts proficiency. They have a complete understanding of the techniques and principles and have a high level of proficiency in them.
"Blue Core": This rank represents someone who has surpassed the limitations of their core and reached a high level of power. They have a deep understanding of their core and are highly proficient in using it.
"Indigo Core": This rank represents someone who has reached a level of mastery that is considered almost otherworldly. They have a deep understanding of their core and have a high level of proficiency in using it.
"Violet Core": This rank represents someone who has dedicated their life to mastering their craft and has attained a high level of physical and mental discipline. Their core is pure and radiant.
"White Core": This rank represents the ultimate level of power and mastery. The martial artist has a completely pure and stable core, with the strongest and most controlled energy. They are considered the strongest and most elite martial artists in the community.
This ranking system is based on the color of a martial artist's mana core, with black being the weakest and white being the strongest. It evaluates the proficiency of a martial artist in the techniques they have learned, based on the purity and control of their mana core.
Just to explain, even to break through each stage you need to have sufficient degree of control over mana to extract impurities and rank up, which requires exp in terms of whatever martial art they are using.
As for the wizards, they use a different system, they dont form core's rather they create rings or chains around their heart, the notations are different for each kingdom within the west continent.
The ranking is pretty simple from 1-chain to 9-chains, i don't believe i need to explain more on this as this is pretty much the standard.