The difference between before and after is more the difference between de jure and de facto.
We haven't had a criminal prosecution of a President for official acts, no matter how illegal or even how evil for over two hundred years of Presidents, and we've had no shortage of shit worth prosecuting.
Like... I'm much more in line with the reasoning and even the tone of the dissent here, but the ruling is essentially codification of pre-existing practice. Which is, I guess... worse given incentives, maybe? But the incredibly wide range of immunity especially for the worst acts of Presidents has been pretty long standing and already baked into the cake of expectations by those who hold the office.