The presidency gained expanded immunity not expanded powers. He can give the CIA illegal orders without fear of prosecution, but the CIA is not bound to follow them.
That's the key difference in how this change impacts a Biden Presidency, and how it would impact a Trump presidency. Biden has surrounded himself with people who respect the law, while Trump will surround himself with criminals, lackies, and cultists.
Michele Obama is the only one consistently beating Trump in polls. Not that I want Obama v2, but that's where it stands currently.
Done properly, a replacement would get a big bump with the nomination, but that's not much to count on.
Jon Stewart would probably wipe the floor with Trump if anyone can figure out how to draft him.