The atomic bombs certainly played a part in Japan surrendering, but it wasn't the only one. They were also facing a land invasion from the Soviets, had an utterly depleted military, waning support from the public, and a potentially devastating land invasion by the US on their doorstep.
>You are saying magnitudes don't influence the identity of something, this is obviously not true.
I am considering these things very dryly and very objectively. I am putting aside emotional pressures and processes and only considering the results which are ultimately all that matters. We already know how much damage an ill-willed intelligent being can achieve, we already know how much more efficient computers can make certain tasks. "AI" is not a "gravest of dangers", given that knowledge.