Article II says no such thing. Humphrey's Executor established a useful compromise between "the Constitution is silent on removal" and "come on, is it really impossible to fire a postmaster?", but Trump has chosen to defect from that compromise so I no longer feel bound to accept it. Until he reinstates all independent agency heads he's purported to fire, I don't accept any removals he performs without explicit authority as legitimate.

if a court overturns or reinterprets that, then it is the law. America is a common law country, not a civil law country. The process of litigation and court precedent is how laws work in a common law country, so I don't see how your framing of the situation is really all that valid.