So, cracking the atom is a fundamental breakthrough, because we simply couldn't do that before. No matter how much money you spent, you could only exploit natural atom-cracking in radioactive decay - you could not vary the rate. So that was a fundamental breakthrough. Going from A-bomb to H-bomb, not so much (we could always just use a couple A-bombs where we could now use an H-bomb).

H bombs would seem to be a different fundamental breakthrough than atom splitting. The similarity is their engineering application more than their fundamentals.