Well, technically Greyback got what he deserved. He mostly likely died in the Battle of Hogwarts and if not he was probably dementor kissed. Umbridge only got into Azkaban.
Ok let’s pretend that Greyback’s fate is that, and not ambiguous, wouldn’t the punishment fit the crime? I mean what Umbrige did warrants punishment but death? That’s not proportionate. Greyback was literally a mass murderer and people eater.
@MarioKartWiiYes MarioKart7No She made Draco and others spy on students just to see their private... adventures, shall we say? AND she most likely jinxed the quill she made Harry use in Order of the Phoenix to write "I must not tell lies." Whereas Fenrir Greyback only killed people because, like Remus Lupin in his early days, couldn't help but give in to the temptation of which to perform the acts of a werewolf. Does that answer your question?