Is Yang Junmo lacking?
Of course not, but he is missing something that everyone else has.
Ambition.
When Su Chengyu first arrived at Capital City, Yang Junmo already possessed the means to assault the Nascent Soul Realm.
But Yang Junmo did not do so. He neither pressed his domain nor thought about undergoing Tribulation. As Capital City's most carefree young master, Yang Junmo didn't take the matter of improving his realm seriously at all.
The reason for this outcome is eight parts similar to that of Lin Ran from the Lin Family, who chose the Demonic Path.
It is because at home, apart from himself, there is an elder brother who is far more dazzling.
However, under pressure, Lin Ran chose to join the Demonic Path, taking a deviant path with his sword, while Yang Junmo opted to thoroughly throw in the towel.
Of course, even so, Yang Junmo remains a leading figure among the young generation.