I think it’s important to distinguish DSM Sociopath (Joffrey) from Gervais Principle Sociopath (Cersei).

Both abbreviate to “sociopath” but they are very different concepts.

I don’t think Joffrey qualifies as a GP Sociopath at all, as GP notes. While he was “in charge” he didn’t play the GP Sociopath game, and so was quickly removed. As the OP notes it’s possible for Clueless to be placed in positions of power in plenty of cases, for example when a fall guy is needed, or a puppet. So just wearing the crown doesn’t mean he MUST be a GP Sociopath.