not to lessen your ideal, but both sour and bitter fall into a category of complex flavors.
I absolutely agree that good coffee is a balance of sour (acidity) and bitter, but I take acceptation to the idea that it's a balance betwen these 2 flavors;
a coffee can be both very sour and very bitter!
Consider - nearly all of the complexity in coffee is from the development of acids as the coffee is growing, and the conversion of amino acids and proteins during the roasting process (Maillard reaction) of the bean;
if you over roast the bean the coffee will breakdown too far and develop carbonates, which are both cancerous and unpalatable. That's one type of bitter.
Coffee that's roasted a little less (but still far too much) will contain a campfire note (smokiness).
In both of these instances, good acids (which cause sourness) such as malic, tannic, and citric, are broken down - while less palatable acidic compounds such as acrylamide are produced.