Is there a differnce between 'Classic Rock' and good rock that just happens to be old?
You have to realize that, at one point, rock was the pop music.
And in the same way that pop music is made to try and appeal to as many retards as possible, rock, at one point, was the mainstream and was produced to appeal to as many people as possible. This, is the essence of Dad-rock.
There are plenty of artists from back then who were exceptionally good, just like there are plenty of modern artists who are exceptionally good.