In his training, Theo learned three major powers. The first was related to his Reality Eyes.
After seeing other people's status, Theo had been experimenting with his Reality Eyes to see what they looked like. To his surprise, not only the skills, but he could also see their description, allowing him to grasp their power.
And when he took a closer look at the skill's description, he realized that Theo's power was beyond his imagination.
The Order itself could affect him, his surroundings, and the people around him, including his enemies. That was why when he looked at them, he could see the upgrade requirement of their skill.
In other words, Theo found out that every skill could be upgraded. The system itself had existed from the beginning. The only reason why no one ever did it was that they never realized such a system existed. If they knew that they could sacrifice some skills to upgrade their power, they would have done so.