There is a major distinction between actual dynastic rulership and the Kims as heads of state in the DPRK in that the Kims were all elected and do not have absolute power despite what western propaganda would have us believe. Dynsastic rulers are given their power purely by virtue of their blood regardless of popular support whereas the Kims each had to earn their positions by demonstrating they could be trusted as leaders. And they are trusted by the party and by the people who rightly associate them with the successful resistance and then deterrence of imperialism, the kind of imperialism that wiped out almost one third of their population still within (just barely) living memory. The Kims’ leadership is not automatic by blood, it is contingent on their ability to be good leaders, but it would make sense that as leaders, they would do their best to train and prepare their children to be good leaders as well, and it makes sense that the Korean people would trust them, given their history. There is a much stronger case to be made that the Bushes and Clintons are dynasties far more than the Kims.

See also: https://leftistcritic.wordpress.com/2018/02/17/the-myth-of-the-kim-dynasty-the-reality-of-democracy-in-juche-korea/