In the evolutionary path, legacies were very important, and so was the master.
A legacy was like a book; one had to read and self-study from it. When one was stumped or reached a bottleneck, they could only rely on themselves! Sometimes, they would be stuck at a critical point and wouldn't be able to figure it out for the rest of their lives. But with a master's guidance, they could come to a realization with just a simple mention!
Moreover, a master could understand his disciple's evolutionary progress and understand what problems his disciple encountered. He could guide him in a targeted manner, making the speed of improvement naturally different.
Xu Jingming and the others were self-taught! After stepping into Lv. 5, their improvement became slower and slower.