Aristotle’s argument is beautiful and simple, but I’m not sure I buy it. Is it not possible to conceive an excellent human life in which happiness is not the end result? Perhaps you are very good at that ultimate thing for the sake if which you exist, but nonetheless live an unhappy life. It’s a bias ancient philosophers had… that we, humanity, are special.
Either way, you have to appreciate Aristotle’s attempt. One thing that really struck me was the similarity to Heidegger’s concept of one’s “ultimate-for-the-sake-of-which”…from which all other things get meaning.