So in your conundrim, Lire, I would probably go with Mussolini simply because of his impact on history. I don't think putting certain leaders next to one another is insulting at all. You have to also understand that what we think of one leader may not be what others think of that leader, especially people who were contemporary of that leader. While we might look upon Genghis Khan as a great leader, or Alexander the Great the HORRORS they were responsible for are utterly disgusting and inhuman (let alone inhumane), so there are different ways to look at it.
There is still a difference between Hitler and, say, Genghis. Having Hitler as a leadr for Germany is insulting because he is not considered a great leader by the Germans, he is a leader that mostly brought shame on Germany (you have to agree that the damage Hitler made to Germany's reputation in th world is huge). Genghis Khan, on the other had, was also ruthless and killed lots of people, but lived in a totally different epoch, when countries would go to war just so they can humiliate their neighbours and conquer more lands, and didn't care much about commiting atrocities. That's why Genghis is considered a national hero in Mongolia. The question whether a certain leader should or should not be added depents on his nation's attitude towards him. I wouldn't put Mussolini as an Italian leader (in fact, I didn't put him in my mod) because he is not considered a national icon in Italy.
I also disagree that every civ should have leaders who represent all stages of their history. There is nothing wrong in omitting a certain era, especially the modern era (by "Modern" I mean post-Napoleonic).