I cannot class a psychopath such as Ramsay as being more monstrous than a fully capable person such as Walter White who defaces his humanity to become psychopathic.

To me, a monster must terrify, there must be this element of horror. Psychopaths don't really terrify me, because I see them as disabled human beings.

American pop fiction paints them as devious evil masterminds, but really they have measurably less functional brains.

This is likely where our disagreement stems from. I imagine you see psychopaths as more 'abled', mysterious even, but I see them as less 'abled' humans. They suffer from genetic or even physical brain damage.

A psychopath is ultimately a more predictable opponent because they lack a few mental ingredients which makes them less complex. I would deal with a psychopath in a similar fashion as dealing with a fire. Both could easily kill me, but they are so obvious. They are simply not as formidable as a fully aware and capable human being like Walter.

Walter could be your best friend, and you'd never know what he was capable of until you found yourself in his way. Ramsay could be the best friend of the village idiot, everyone else would treat him with extreme care.