You falsly assume that the intent of people building that device was to make it efficient - it wasn't. They wanted to make sure the fuel, heated up to the right temperature, will yield energy gain and that happened.
You can think of a this as test flight with a plane model vs. building the actual plane. We needed to test the aerodynamics and see if this flies at all, it worked, and now it's the time to build the actual plane. Someone has to do that test at some point. Would make no sense to build a plane without knowing if it's going to work.
