[zugi]

You are right that no one knew that Space X's approach would work until they demonstrated it. However, it was clear that the shuttle's "reuse" approach was a dismal failure early on - even before it was built, the sheer mass shuttled to and from orbit every time was a giant red flag to anyone who understands the basic rocket equation. That also drastically limited its altitude and usefulness. In a world where practicality matters, it should have been abandoned early on in favor of a return to expendables, until we figured out something that actually worked.