Reality check: this was the only ruling the Court could have come up with

[ScratchCat]

18. More from the dissent

In sum, the majority today endorses an expansive vision of Presidential immunity that was never recognized by the Founders, any sitting President, the Executive Branch, or even President Trump’s lawyers, until now. Settled understandings of the Constitution are of little use to the majority in this case, and so it ignores them.

I've seen others who read the decision mention this too - they didn't even argue this in the appeal.