Well, they were not exactly wrong. Humanity as a collective would have been able to push the technology to a usable level in that timeframe, the knowledge for

Well, they were not exactly wrong. Humanity as a collective would have been able to push the technology to a usable level in that timeframe, the knowledge for that was certainly there. But it would have required spending quite a lot more money on it. The incentives for that were simply not there, and that remains still true today. With the current level of investment and committment, it's more like 40-50 years for the first real generator, and another 10-20 until the first commercial one.