That doesn't make it any less contemporary or cheap. They are operating today, and they cost less. If your goal is to get mass to orbit for the least amount of cash, that's all that matters.

There's also the march of technology to consider. 1970's technology isn't going to be cost competitive forever, even with amortized R&D costs. When SpaceX gets to the point of delivering complete reusability, there's going to be a shakeup.