That opinion specifically defers to lower courts to define the precise limits of the President's immunity. I refuse to believe that the collective effort of the judicial branch would construct those limits in a manner that enables dictatorship.
The lower courts can be appealed to the higher courts, so the opinion of the supreme court was effectively that the president is immune if they say so, on a case by case basis.
It was a clever but blatant way to give their side immunity without giving it to Biden
You're correct that the Supreme Court ultimately has final appellate jurisdiction on matters of immunity, but that's a long way from enabling dictatorship.
To get there, we would need to assume that the Supreme Court, including only 3 Trump-appointed Justices, is both unwaveringly partisan and unwaveringly supportive of dictatorship.
The Supreme Court is unwaveringly partisan and corrupt; its members have taken bribes and invented new rights for Trump to keep him out of jail. I wouldn't assume that they'd reject a dictatorship.
We’re just gonna pretend Trump v. United States, 603 U.S. 593 (2024) doesn’t exist, are we?