“So the only real difference between the first and the second case is that the H-bomb is smaller, much more expensive per amount of energy released, and explode

“So the only real difference between the first and the second case is that the H-bomb is smaller, much more expensive per amount of energy released, and explodes inside a chamber” - that sounds like a major technological breakthrough to me. They managed to concentrate so much energy inside a chamber in a controlled manner.