In a lot of ways, they vested practically nothing in that branch. It's by far the shortest section of the Constitution, which basically comes down to "Supreme Court: We oughta have one."

They made up their own powers. There's nothing about judicial review in the Constitution. They basically decided that they had that power, and everybody else agreed with them.

https://en.wikipedia.org/wiki/Marbury_v._Madison

So perhaps their greatest mistake wasn't vesting too much, but vesting too little. That left the court open to write its own job description. And also to create lifetime appointments, in theory to de-politicize it, but in practice to enshrine ideologies for many decades.