Economic viability is not the same goal. One is a business goal, one is a scientific/technological one. The goal from the DC-X 35+ years ago was the latter. Certainly, we'd expect the economics to improve since then.

The technological viability was shown with the proof of concept. If you meant strictly economic viability was unknown, I agree with you. This isn't meant to disparage SpaceX. They're doing great. I would say there is a risk that isn't often talked about which is the quality risk. Early on, SpaceX disregarded well-known quality control checks, presumably because they didn't think they were worth the time/cost. When that burned them, they integrated those checks. Do that enough times, the economic viability erodes.