Depends on where and when you are. Not every kingdom practiced primogeniture and several places and time periods had ways to remove people from the line of succession. Even when they didn’t have any of that, civil wars to put a more well-liked person on the throne were a thing. Cleopatra’s faction trying to crown her over her less competent brothers, for example.
was it really like that? does anybody have more knowledge in this field? or is this just a flawed prejudice?
Depends on where and when you are. Not every kingdom practiced primogeniture and several places and time periods had ways to remove people from the line of succession. Even when they didn’t have any of that, civil wars to put a more well-liked person on the throne were a thing. Cleopatra’s faction trying to crown her over her less competent brothers, for example.