I could see Green Ghost being like Dupli-kate, hiding the source of their power so they do not lose it/die.
The reason there is no new green ghost is because the gem is sitting in a safety deposit box in Arkansas.
As to the usual "why not use the transporter to pull a Thanus?" Nolan is 10,000 years old, his cellular structure is probably too complex for the teleporter to penetrate, let alone lock on to.
Donald being xeroxed is dark as hell, since the robot body thing is a new development, what the hell were they doing to him before?
It also shows that Cecil has a dependence on Donald, a friend would have let Donald die, Cecil needs him BACK TO WORK.
My impression isn't that he's a Kenny, he's a highly effective agent who gets sent in when no one else can handle the threat level. And since he's not powered, a lot of those situations are too much, even for him.