> think Maximus, Achilles or Michael Jordan

Maximus is a bit of a strange choice there. Marcus Aurelius of Meditations fame, is the titular grandfather figure in the film (right at the start). Meditations has a lot in it about child rearing and Marcus was something of a devoted father to his many children (for Roman men in those days). All that said, his son, Commodus, the first emperor to have the title passed down to him from his own father, was a uniquely terrible person. As seen in the film, he was just a 'very bad guy', but in reality he was much worse than is portrayed.

In essence, no matter the effort you put into your kid, they are still themselves