This was always an issue in Rome. People were afraid their heirs would turn out to secretly be wannabe dictators, and you couldn’t do anything about it since you were dead. How would you go about making sure your heir was as close to your vision as possible, both outwardly and in their desires should they be emperor?
In ancient Rome, the sitting emperor often would choose a successor from, well anybody really, often not even a relation. They then adopted that person. If one has to have hereditary rulers, this seems a fairly sensible way to go about it.