The whole point of the Bill or Rights was protect individuals and minorities against the tyranny of the majority. Dred Scott was not merely a failure in this but a complete betrayal, and had a crucial role in the start of the Civil War.
The presidential immunity ruling is also a horrible ruling and sends all the wrong messages. However, it is not the complete presidential carte blanch that it is made out to be, and the threat of later criminal prosecution has never been one of the major checks on presidential power and overreach. Executive actions can still be struck down by the courts, legislative actions can still still be passed and vetoes overwritten, impeachment is still on the table, people can refuse to obey illegal commands, and most of all the all the electorate can choose not to vote in would-be dictators. Frankly, after all the that Trump has done, if the people vote him back into office, then a strongly conservative SCOTUS is the least of our problems and we have only ourselves to blame.
So, yes it is a very bad ruling but it is no Dred Scott. We continue to be a free nation which is more than we could say after Dred Scott without putting one of heck of an asterisk after the statement. However, as always, this freedom must be earned and held onto to. So, in that sense, the presidential immunity has changed nothing.