In many calculations, E IS used to denote Voltage and it has been for a very long time. I have seen it used this way since my Physics class in 1974. Any subsequent training in electronics used either E or V, depending on whose books were used. E is used because it stands for Electromotive Force, which is measured in Volts, as you know.

You seem to be looking at current via the calculation but the rate of electron flow depends on voltage and resistance- ‘current draw’ is commonly used, but i think ‘flow’ is a better word- if the resistance is high enough, it’s definitely not being ‘drawn, especially since Voltage is equated to pressure. Electrons move through a conductor or circuit at a rate determined by its resistance and the voltage

Yes, I know an amplifier is a voltage source and if you read my first comments about the original question, I made that clear.