Alderaan was a powerful telemancer and with the help and assistance of Solar Blyze, the young king figured out the reason why he could read the minds of countless people without even batting an eye.
The mages could be all Level 10 Telemancers and Alderaan would still be able to read their minds because he was the son of the original Mind God, Rasmus. Solar Blyze revealed the truth to him when Alderaan was eighteen.
By that time, Alderaan was already occupied with taking the role of the king and he considered Therius more of his father than his real father, that all that mattered to Alderaan was becoming king of Akkadia and creating a legacy that would make everyone proud.
If he could blot out the mistakes of Therius, then he might have done it. However, Alderaan knew that Therius had not been perfect and was actually wrong in so many ways, even though some good came out of it.