The only thing that holds a voltage without current flowing through it is an insulator.

This isn't even wrong. A voltage can be present without a current flowing. Touch any live wire to get an instant demonstration that there indeed was a voltage present even if no current was flowing. Not because the wire is an insulator but because it wasn't at that point in time conducting any current. Your finger (also not an insulator) closing the circuit however and then allowed current to flow.

Ouch, you need to take another look at that.

The definition of an insulator is a material that holds (up to some amount of) voltage without electrical currents appearing.

Your example needs two wires. And the wires themselves don't have any voltage. All of the voltage is between them, and is only there because they are insulated from each other.

No, the definition of an insulator is a material that doesn't have the ability to carry current because it has no free electrons.

You are conflating 'insulated' and 'insulator'.