They seem to have stopped training new astronauts in the later seasons. I can't believe Ed is still a character, let alone in command of a mission in deep space. I agree the whole show has gone off the rails since season 2.
I think Ed's arc is plausible in its frustration. Office politics are a big deal IRL. A global hero like that could use his political capital to talk his way into the role of his choice, even if he really shouldn't be there.