This is a question that I think is impossible to answer--there were no clinical assessments of something like sociopathy until the 20th century. It's very difficult to get estimates of historical crimes other than murder (see here); I'm sure it's harder still to work historical rates of illness. You can find lots of threads on here that are basically, "Have historians figured out what this person died of?" and the answer often is, "Well, there are a couple of different theories. We think this is the best theory now, but thirty years ago we might have said something else." I wrote one of those on "The English Sweat", which is likely an otherwise unknown form of Hanta virus, but it goes into how even when we're pretty sure people died of a known disease, we're often not sure based on description which known disease it was based on descriptions. Now you can imagine how much harder this is both for mental illnesses and for figuring overall rates of these diseases.

One thing I will add is that most people in Medieval Europe would have been peasants. As a general state, we can say our lives today are much more atomized and individual than life was for people in the past. Peoples's identities were often nested within ties of family, community, and even hierarchy (landlord/local notable had certain responsibilities to his peasants just as they had certain responsibilities to them). Even today when I interact with people in, say, Turkey, it's hard to explain that just because someone's uncle is rich they are not also rich. Life was, in general, much less individual. This is likely a high point, or near a high point, for individualism and anonymity in human history.

As we transfer from a mostly agrarian society to an increasingly industrial society due to early scientific farming methods and the industrial revolution in the 19th century, we have an increasingly urban society. 19th and early 20th century thinkers are all about this, how society is changing, how people are less embedded in a community or, alternatively, conceiving it as being simultaneously being more weekly embedded in more communities. Marx talks about this as "alienation", Simmel talks about how we are embedded in multiple communities in his "Metropolis and Mental Life" and how this is potentially freeing (not alienating), Durkheim talks about the transition from "mechanical solidarity" to "organic solidarity", and so forth. This doesn't necessarily mean anything for sociopathy, but I just want to highlight it to show that tough times in some social structures may mean not more greed and individualism but more relying on communal and familial ties. People generally married within communities, lived their whole lives within communities, and their reputations within those communities were very important and tied not just to their individual actions, but the actions of their families. Social control within communities and families was generally higher, and also took different forms (or at least, that's what a lot of historical sociologists have argued). Again, I am saying this only very provisionally, but there was a rather large change in social structure in the 19th century with the rise of a more urban and industrial capitalism that 19th and early 20th century thinkers were trying to grapple with. Any attempt to answer this question (and again, in the first, I'm not sure a definitive answer is really possible) I think needs to keep that change in mind.