[Robert DeLong]

Not quite true that a judge can only be removed by impeachment process.

Removing Federal Judges Without Impeachment

However, it is still quite hard to remove a judge, especially based solely upon a decision he delivers.

[Mariner]

No federal judge has been removed by any process but impeachment.

The professors who wrote the article you linked stretch the constitution to suggest congress COULD pass a law to allow their removal without the impeachment process.

But it’s certain that would not pass “judicial review”.

[Nateman]

During the First Democrat-Republican War William Matthew Merrick was removed by dissolving his court underneath him. It was then reformed without him!