I want to add that experimental reactors used for scientific research might never become net energy positive and that would be fine. Their purpose isn't to generate profit, it's to learn more about the physics, so it will be more valuable for them to be adaptable than efficient.

However, that doesn't mean that you can't take a configuration that has been shown to have potential and make a reactor that is more efficient than adaptable and use that to generate power for the electrical grid.

Basically, they have two different purposes.