One of the requirements a mage had to accomplish before they could advance to a Magus, was understanding a domain. Once they succeeded, then they could finally take the last step and be promoted.
To advance into the Arch Magus, a Magus had to create a unique move. It could be an offensive move, defensive, or even a supportive move as long it was unique to them, then they could advance.
However, advancing into the Legendary realm seemed easier compared to the latter two. But in fact, it was far more complicated because one had to have a deeper understanding of their innate magic.
That was the only way an Arch Magus could advance. It was also the reason Kyran told Tritus to learn all he could from Osric during their fight. Because what else was a better way to learn and understand one's innate magic than during a fight? Aside from this, learning from Osric who had the advantage with mage level was beneficial to Tritus.
