I believe Aristotle’s definition of the highest good being happiness makes sense as you can’t any further than why you want to be happy. Of course, said actions to achieve happiness have to be in line of a virtuous life much like Kant’s restriction on the good will being in line with duty. However, the goal is to achieve happiness in Aristotle’s view on the highest good, which is why it is impossible to sacrifice it. Kant’s categorical imperatives can be put against one another by having conflicting duties which is why I believe Kant’s definition is less reliable than Aristotle’s.
While it can be argued Aristotle’s view also has holes, such as what determines what is prudent, to which Aristotle’s responds role models who possesses virtue. This is to say there is an external influence, that being society, that determines if an action is virtuous or not. That being said, I do believe in ethical relativism so it would make sense that the society one is raised in determines how you view certain things morally. It is more understandable than having conflicting duties for one individual that may not even lead one to a life