I mean, that's what this comes to, right? If he ordered Seal Team Six to storm Mar-A-Lago to recover classified materials with deadly force, then he's operating in order to maintain national security via his authority as Commander in Chief. That would be legal under this ruling, correct?
I get that would lead to an actual civil war, and I get that their argument is important to shield the office from neverending frivolous lawsuits, but in being forced to rule so explicitly on this it seems like they've opened the door to political assassinations. All a President would need is a willing wing of the military and a superficial rationalization and there'd be nothing a court in this country could do about it.