In the script obtained by He Tiantian, Jia Jing was not overly interpreted, he was simply obsessed with the pursuit of immortality.
Becoming a scholar was just to give an explanation to the family, to prove that he had once contributed to the family.
Having achieved the title of Scholar demonstrated that the people of the Jia family could switch from military to civil pursuits, and he had also provided a son for Ningguo's Mansion, thus fulfilling his mission.
Therefore, he willingly handed over his title and position as the clan leader to his son, and went off to pursue his own dreams.
Engrossed in alchemy, dreaming of immortality, he neglected his entire family for his own sake, allowing his descendants to engage in misconduct and ignoring the misdeeds of his relatives.
Even if Jia Jing was not a villain, he was hardly a selfless good person.
Yet He Tiantian was quite satisfied with this setting, because a person with flaws offers more room for development.