Despite the countless "great" movies after Rocky, it still manages to be one of the few classics that stand above majority of the great "modern" ones.
I have not seen Rocky, but with your perspective to it's impeccable standard, even at its time, there's now a little more light shone on why it is still one of the great classics.
As you have said, the directors and writers may not have they forever a work of art, but Rocky seems to be standing firm.
Exactly, it's basically lightning in a bottle... Amazing film