> while the Supreme Court says “unofficial” acts are still prosecutable, the court has left nearly no sphere in which the president can be said to be acting “unofficially.”

Agreed, this is a key function of interpreting the law.

If the people don't like a landmark case (i.e. the disagree with the interpretation), Congress can pass a new law. If a new law contradicts the court's opinion, the law takes precedence.

But, they didn't invent any new tests here. Baseline, what they want to achieve is to stop the prosecution of Donald Trump in its tracks, and they'd like to use no more and no less overreach to achieve that. If it comes back to them, and they need to hammer harder, they will do that. But, the key goal is to protect Trump.

So, they can invent tests later, after they see how this decision affects the prosecution.