I would disagree with you, not in the aspect of NK being able to inflict tremendous damage on SK; nobody needs or needed to be reminded of that. It is no secret. There has been plenty of Cong testimony that such an outbreak of war would be horrific and I have no reason to doubt that.
It may well be a true truth that Trumps’s bellicose stance against NK was more bluster than reality; However, the statement IMO *DID* need to be made that NK would face utter destruction in the event of a missile attack on the US or territories. The rhetoric employed *did* elicit a response from China which might be revelatory to those watching more closely than you or I. IMO it also generated sort of an air pocket in which Kim Jong Un can say nothing for a period and not quite look he’s backing down.
So as a tactic, I consider it to have been useful. For the tactic to be useful, Kim has to take it seriously. If Trump’s top adviser comes out and claims “he’s just bluffing”, unless I’m missing the reverse one-and-a-half-gainer strategy (very possible) it’s a piece of Bannon undermining Trump and at the same time, a ratification of this leaking thing for NPG No Possible Gain.
Thus, I don’t agree that Bannon’s firing is stagecraft. At least so far.
IMO, the timing suggests that Bannon's "leak" may well have been made after there was good evidence or actual assurances that China successfully convinced NK to not act irresponsibly. If so, the leak was intended in part to calm the concerns of various observers. Ergo, there was no undermining by a subordinate.
The "bluster" was most likely phrased in such a way as to be unmistakably understood by potential adversaries after the translation. Bear in mind the speaker is from New York and facing some rough players.
As for stagecraft, both of the actors are quite skilled in that regard. Reportedly, Bannon was there longer than he had intended and had submitted his resume weeks ago; one could easily conclude the separation was mutually delayed so as to not be disruptive.
It should be clear in the coming weeks which of our two views is the more likely.