2 is arguing that Congress hasn't sufficiently defined the powers of the SEC, thereby giving it an illegal power to "legislate" for itself. I think 3 is saying the President needs more power to appoint and dismiss SEC judges (i.e. restrictions on the removal of the judges impedes on Prez's responsibility to take care that the laws be faithfully executed).
2 is arguing that Congress hasn't sufficiently defined the powers of the SEC, thereby giving it an illegal power to "legislate" for itself. I think 3 is saying the President needs more power to appoint and dismiss SEC judges (i.e. restrictions on the removal of the judges impedes on Prez's responsibility to take care that the laws be faithfully executed).