I just have this image that he has to be smarter than he appears to be, and very special in someway other than just as a killer... no way would even Kronos have put up with him if he had no improving features!

not to mention surving 3,000 years of change... he might be a psychopath... but he would have to be a very special one

and now with the image of him and Silas as spoiled kids I suddenly had an image of him channeling Sheldon from big bang theory and saying:
"I am not insane, my mother had me tested" and pointing to Methos