Thomas has attended at least two Koch donor summits, putting him in the extraordinary position of having helped a political network that has brought multiple cases before the Supreme Court.
Team Red controls the house, and the house would have to be the body to start impeachment hearings. Why would Team Red remove a judge who is being bribed by Ream Red backers and decides cases in favor of Team Red?
The US "checks and balances" system was never designed to deal with this kind of problem.
The executive can't do anything. Half the legislative branch is controlled by Team Red. Team Red would have to be willing to hand a loss to Team Red for there to be any accountability. A weak leader is going to be much less willing than a strong leader to hand a loss to Team Red because it would be the end of his leadership, so without an election handing over control of 2/3 of the government to Team Blue, there can be no accountability.
And, even then, with the majorities required for impeachment and removal, you'd have to convince a significant fraction of Team Red to defect and take a loss, when they can avoid a loss by just holding the line.
The US system's checks and balances are broken and unable to deal with this scenario.
Not setting a limit on the number of Supreme Court judges was an oversight, not a clever trick they came up with to allow the executive to collude with the senate to put an unlimited number of judges on the Supreme Court.
Sure, but you can't remove a judge except by impeachment. So, if you said the supreme court was now 3 judges you'd effectively be getting rid of judges without using impeachment. Whether that's legal or not would probably be decided in court, which would get challenged all the way up to... the supreme court.
The law is clear, a Justice can only be removed through impeachment. If Congress were to reduce the total number of seats as has happened a few times historically there simply would not be a new Justice appointed after one passes or resigns.