This doesn't say the executive is above the law, it says you can't prosecute the president for doing his job, just like you can't prosecute judges for their rulings on the bench or members of congress for their votes on the floor.
The equivalence is that in all three cases those are the official duties of the office.
I would agree that the scope of the president's job description has gotten overly broad over the last century as congress has delegated more and more of its powers to the executive branch, but I don't think a prosecutorial Sword of Damocles is a good solution to that problem. Certainly it's not the constitutionally prescribed one anyway, which is what the court's ruling affirmed.
