If you look at how airplanes were developed, that theory doesn't hold water. They were developed everywhere, following their own paths, even if some basic things ended up the same. But then again, if you look at birds or insects, they also share a lot of flying related details among their groups. It simply take some basic things to fly, but otherwise different inventers did what they wanted. Peer-evaluation is also concept fitting for science and relatively modern engineering in companies (or institutions). It doesn't apply to the kinds of brilliant visionaries airplane design relied on for a long time during its early development. Just like Tatsuya doesn't need anybody to evaluate his inventions.
If gravity control had been needed for fusion, then it would have been developed already, even without a single high schooler. Unless we are supposed to be believe that the world never had a single decent magician before Tatsuya was born, and thus there was nobody around to invent anything worth mentioning. Ironically enough this very episode proves that wrong with the relic even Tatsuya is unsure he could replicate because it's so complicated craftsmanship, meaning brilliant magicians capable of creating such things existed already in the ancient past.
Shinta's theory seems like something that would obviously greatly benefit a lone inventer, but multi-million research teams would be able to deal with it sufficiently.