Actually yes, in many respects the sport's national impetus was gained by the Cape Epic's reputation and international status. Through that many people, who will never ride Epic, have discovered an awesome sport. Over the years the sport has seen growth and maturity beyond the endurance sufferfest of Epic.
A good example is Burry Stander. He was an exceptional XCO racer with many accomplishments ahead of his Cape Epic titles, but he only became more widely known as an athlete and after winning Epic. This also brought XCO more into the fore for riders.
Platt is another example, he was a consistent top ten finisher in World Cup XCO, wins Cape Epic and suddenly everyone locally and in Germany know who he is.
Cape Epic gave an injection of broader appeal to South African MTB, locally and abroad. This is a fact. It doesn't mean it's central and all encompassing to SA MTB, but it absolutely has played a role in the growth of the sport.