By this definition, a human would be considered a schemer if they gamed something analogous to a training process in order to gain power.

Let's consider the ordinary process of mental development, i.e., within-lifetime learning, to constitute the training process for humans. What fraction of humans are considered schemers under this definition?

Is a "schemer" something you definitely are or aren't, or is it more of a continuum? Presumably it depends on the context, but if so, which contexts are relevant for determining if one is a schemer?

I claim these questions cannot be answered using the definition you cited, unless given more precision about how we are drawing the line.