I think there may still be merit to the op’s case that we should distinguish between the risk of a nuclear attack and the risk of a nuclear exchange (or, “nuclear Armageddon”).

Some of the scenarios I outlined—rogue non-state actors, regional wars—may lead to isolated nuclear attacks but not full exchanges. I’m not sure if the hydrogen bomb distinction is relevant here.

(Yes, afaik what you say is true, but I think this is sort of a red herring.)