General Milley have for 'going rogue' if this was all about the politics of some imaginary "Deep State"?...they had already won...just needed to make sure an Uber driver was available for Donald and Melania on Jan. 20th.
Face up to it...unlike other Presidents, who when they've lost an election, simply pack their bags and find something else to do, like plan a library, or build homes for the disadvantaged, or perhaps even paint or play golf...Donald Trump, being the epitome of a malignant narcissist, and having nowhere else to go (his business 'empire' is deeply in the red and facing enormous debt repayments, plus he's also facing multiple civil and criminal trials), is literally terrified of what his future has in store...so, having zero concern for anyone else's well-being (again, his malignant narcissism), while still in office he was a clear and present threat to create a military crisis that might allow him (in his mind) to remain in the WH and never have to confront reality...hence the concern of General Milley (and Mark Esper...and Bill Barr...and a lot of others in D.C.) after the attempted coup on Jan. 6th...which, btw, you sort of 'glossed over' in your "analysis" of what's transpired.
Bottom line...no possible rationale for Gen. Milley to call the Chinese just to get one more 'dig' in at Donald Trump...but there is a strong rationale for a totally defeated narcissist, facing oblivion, to take extreme measures to "save" himself from ultimate Accountability.