It is perhaps not a surprise that a union offical disputes McCain's use of the incompetent federal worker cliche. Procedures do exist to remove workers from their jobs, and many people do get fired.
But it takes a long time, according to the outside experts who follow such issues closely. McCain wisely faults not an individual but a "system." That puts him on pretty solid ground, where even a study by the federal government had difficulty finding supervisors who had attempted to take action against poorly performing employees.