This is a very insightful question. I think this is one of the issues that comes from basing the diagnosis of sociopathy primarily on behavior. First of all, I agree. I am not sure that sociopathy is even a "real thing". I do think it's interesting that there seem to be people that are very similar to each other, but I think that is bound to happen in the spectrum of human personalities and behavior -- that you would be able to find people clumped together in any part of the spectrum. Sociopathy may just be a particularly intriguing segment of personality traits because of the disparately large effect they seem to have on the lives of others and the unique motivations that drive their behavior. Yes, I think that sociopaths brains may look different, but our brains are constantly adapting and are constantly being impacted by our experiences, thoughts, and decisions (caveat, there is some evidence that aspects of the brain you wouldn't expect to see changing in a lifetime are also statistically different in sociopaths than the general population). There's just so much we don't know about sociopathy that I am hesitant to actually come to any conclusions myself about its nature.
Even assuming that sociopathy is a "real thing" (as much as anything can be real), I think that it is difficult to study and understand. There's a chicken and the egg problem in terms of coming up with a diagnosis -- you need to identify sociopaths before you can make a list of their traits and you need a list of their traits to identify them. To the extent that there is somewhat of a history of what constitutes a "sociopath," that helps, but there really is so much variation between even modern researchers in terms of their conception of the defining characteristic(s) of a sociopath. On top of that, everyone seems to agree that environment plays a big role in any gene expression, and particularly a tendency to become a sociopath, with some researchers believing that certain subtypes are born while other types are made.
I personally don't feel like most of my behavior is all of that shocking or antisocial, particularly when compared to certain populations like the prison population. It's interesting that you say that [Eastern Europe] has a calloused population. I've visited other places that have an overall low baseline level of empathy and prosocial behavior (the Netherlands, Israel, Egypt, Vietnam, among others). I don't know what sociopaths would look like in those cultures. My guess is not necessarily any worse than the general population, just like uranium pollution may be difficult to detect in an environment with a high baseline level of radioactivity.
One thing is for certain, sociopaths do not have a monopoly on calloused behavior.