If you think about it, being top dogs in any political system sucks a lot. You simply cannot throw your wheight around because you can if you don't want to risk censure of other high level nobles and accussations of tyranny (and that's a big deal) or you may find that government becomes a living hell because everybody is boicotting your reign.
Even worse if there are other political figures with similar power to you, like the Empress Dowager, because malcontent nobles can turn to her to push their agendas and you may end with a court war soon enough if those same level figures are or becomes antagonistic; which happens in stories dealing with royal succession. To avoid that, it's better to have powerful allies within the court to keep everybody in line, like the Salvatore; even if it means to be pushed around from time to time.
In the end, the Emperor can only hope to do what he can without pissing off the nobles, the Empress or the Salvatore, lest he risk a political mess up of insane proportions.