Scott McConnell points out the obvious:
Bush doesn't fire based on competence. Rumsfeld was far more wrong on Iraq than the State Department and the CIA, so him staying on while Powell left and he CIA is purged proves that the President isn't firing people based on competence.
Power-driven neocon elites may claim and their fans in the non-elite world ("useful idiots" is, I fear, too impolite a term) may truly believe that the CIA is being purged because it is not doing its job and that the only people who think that the president is merely crushing it to his will are liberals:
"Critics of the Bush Administration will undoubtedly portray the current efforts to reform the CIA as a ham-fisted attempt by the White House to crush the Agency's independence and make the body totally subservient to the Administration's policy making." -Art Chrenkoff
But in reality it takes either a large degree of dishonesty or denial (For the elites I think the former, for the non-elite rank-and-file, I think it is the latter) to assert that this is so.
That is all.