You hit that nail on the head. Willard is a sociopath but he never learned how to hide it as well as most sociopaths. What makes him seem so alien to us is that he has no empathy. It's a genetic difference that, I think, actually does make him different from most humans and not in a good way.
Unfortunately, not all sociopaths are Ted Bundy. Many are in places of power. Most are astoundingly good at mimicking empathy.
What makes RMoney so strange is that he is not good at the mimicry. I think that's what's so odd. It's hard to fathom how he got so far without learning mimicry. No sociopath should ever get to his level. But come to think of it, the other silverspoon sociopath, George Dubya, did it. And he also had pretty poor mimicry skills, except for the "good 'ol boy" schtick. Willard can't even pull off the "I'm your fake buddy" schtick.
I know that at least one of RMoney's sons also has the disorder but if any of the others escaped having it, I feel especially sorry for them. I feel it at a deep gut level because my father was a sociopath. I know the hell of growing up near a monster, for most sociopaths are just that, monsters. I have great gratitude for two things - that I escaped at age 13 and that I did not inherit the disorder.