Wiz, I'm sorry to say that you completely misunderstood Fragarach. 

It isn't a blow meant to destroy countries or worlds. It is a blow meant to beat people with those kinds of powers. 

It is a conceptual trick that warps time. Bazett's Fragarach can be used when an enemy brings out their trump card, a supreme ability of theirs, but once that condition is met it's already over. 

It is a top-rate conceptual weapon that alters the chain of cause and effect. It is used as a "reaction" to a super attack, in this case Stein's Resonance, but alters time to strike the enemy before their attack is used. 

Before Stein had even used his Resonance, he had already been killed by Fragarach. This was before his Resonance activated. The heart grabbing doesn't work because he'd already died. Even if it didn't, that's not how Fragarach works. All discounting BB's shenanigans. 

I'll say more depending on how much BB wants to say, seeing as he's better at Nasu than myself.