Pretty much any murderer is worse than that.
And Xizor's the head of one of the biggest and most powerful criminal organizations in the galaxy. Mistresses that have refused to accept that he has dumped them, have ended up being mixed with construction materials for buildings on Coruscant.
It seems highly probable that he arranges murders (and that Black Sun does a lot of murdering in the course of their other criminal enterprises).
I'm not saying Xizor's not bad, just that it's silly to pick **** as an example of 'hard to get worse than that' when talking about a character who most commits crimes worse than that.
I disagree. Xizor leaves his conquests broken and ruined from his attentions and his dark whims. That, IMHO, is as bad as arranging deaths or profit or convenience. R*** is a violation on a deeply personal level, which is difficult even for the strongest and most supportive to recover from. That puts him right up there with Palatine and some f the Sith Marauder Lords in my book.