> Charge of an electron is a concrete fact

It's only a fact in one's imagination, as concrete as a fact about properties of any other thing that can only be measured indirectly.

We have no way to directly measure the charge of one electron, so it's a fanciful claim, or at best an approximation, and not a concrete fact.

Claims about wires can be verified.

> We have no way to directly measure the charge of one electron, so it's a fanciful claim, or at best an approximation, and not a concrete fact.

Are you suggesting the oil drop experiment was invalid?

The elementary charge is impractically small, while it is easy to approximate the "imaginary wires."

So you make the calculations and use some wire length that places the error within your acceptable margin. You use the completely precise, but impractically small value of the electron charge on those calculations.

You also use the completely impractical value of the cesium emission frequency on your calculations for your tabletop amperameter, as well as the speed of light on vacuum (good luck having any "vacuum" around). So, why are people complaining specifically about the electron charge?

Both the cesium frequency and the speed of light are practically reproducible and are used to calibrate instruments. Not so with the elementary charge. (Similarly, in chemistry, nobody would count the quantity of stuff in molecules, they use moles instead.)

Well, I do know that infinite wires aren't practically reproducible.

In physics people talk about measuring single electrons all the time. Electrons can be counted with tabletop equipment made with home-like budget. You can easily add them to up to trillions, what is far from a Coulomb, but still a practical amount of them.