I agree that fonts should not differ too much in size and other important metrics, but if you select a condensed font for example expectations are that you can fit more letters into the same line.

Now of every font would do equal spacing (something that your spreadsheet software could just implement, btw.) what would the point be of having different fonts?

As you are running the system ypu could also just make a selection of particularily equal fonts and remove the rest, if that annoys you.