The central thesis of the case here is just ... wrong. That's not the crux of the dispute. USG always always always maintained official acts are immune and non-official acts are not. That's the easy bit. The hard bit is deciding if an act is official, and SCOTUS just punts on that actual core
so when Trump talks with DOJ officials to drum up an objectively sham investigation for electoral benefit, USG's position was that's not an official act, because ordering sham investigations for electoral benefits is not a proper function of the presidency, but the actions of a corrupt /candidate/
as all-knowing rulers of American governance, they've turned to making more sanguine, vague edicts more akin to what one might find in religious texts and sermons
Why has USG always maintained that? AFAIK, the Constitution explicitly says that legislators are immune for certain acts, but never says that the President is. Are we just supposed to assume that that was an oopsie-oversight and they meant to include the President?