I reject the premise. The President is not a king, he isn't presumptively allowed to fire anyone he'd like. The statute establishing the National Science Board (https://www.law.cornell.edu/uscode/text/42/1863) does not give him any such power, so he doesn't have it.
NSB members are executive officers, the statute is silent on removal, and Article II makes presidential removal power the default. Silence means he can fire them.
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.
Common law countries also benefit from common interpretations of laws, which leads to stability for both the citizens who live and businesses that operate in that country. “Calvinball” is technically possible in all common law countries, as long as you move fast enough for the courts to not catch up. So while you are technically correct, I do not want to live in the version of America where your technical correctness is tested to the limit of its bend-but-not-break strength.