Isn't the same principle [super-position] applicable to the electron?
Yes is is.
Diracs equation gives us the quantum field that describes the electron-positron field. Despite its name, it is not a quantised field. A better name for it would be a relativistic classical field. It is akin to the electromagnetic field. And hence we have super-positions. The quanta of the electron-positron field is found only after quantising the field.
In fact, Geoffrey Chew, a quantum theorist, objected to quantum field theory on positivistic grounds since the so-called quantum field is unobservable. However, the quanta is observable. He advocated instead the bootstrap based on the observable scattering matrix.
How to describe the ontology of quanta is an open question and is usually tackled in the philosophy or foundations of quantum mechanics. Personally, I find Anaximander's notion of the apeiron, the unlimited or indefinite, useful to describe the underlying quantum reality given that after Bell & EPR experiments that value indefiniteness characterises quantum ontology as opposed to classical ontology where value definiteness is taken for granted. It's worth noting that the apeiron is akin to Bohms notion of a beable. It was described by Aristotle in his Physics as:
Of the unlimited [the apeiron], there is no starting point, since, if there were, it would have a limit. Further, it is incapable of coming to be and passing away ... that is why, as we say, there is no starting point of the unlimited, but it is rather the unlimited that seems to be the starting point of the other things, and to encompass everything and steer everything (as it is said by those who do not posit other causes beyond the unlimited, such as Understanding or Love) and is divine. For it is immortal and indestructible, as Anaximander says, as do most of the physicists.
We can then suggestively coin the term apeiriton as a minimal element of definite reality that arises from the apeiron. This would be what we think of as quanta in general terms.