That would absolutely remove the incentive for anyone to cooperate with the government ever again. Such a system would make it nearly impossible to proesecute

That would absolutely remove the incentive for anyone to cooperate with the government ever again. Such a system would make it nearly impossible to proesecute the higher levels of a criminal enterprise. It’s easy to prosecute the foot-soldiers of a criminal enterprise with outside evidence. The leadership of it typically requires testimony from others within the enterprise. So, your approach of eliminating all benefits to criminal defendants for cooperating with the government would *massively* enable organized crime, and would end with a criminal justice system that comes down hard on the low-level members, while giving the organizers and planners a walk.