The car manufacturers are well aware of what their vehicles achieve in real world usage.
It would be trivial for them to give and prospective buyer indicative ranges for any particular geographical area.
The actual number of the EPA range is imaginary, yes. But it's useful for comparisons.
But if we're talking about comparisons between two vehicles, the vehicle with a 122kWh battery and a 280 EPA range will go less far and is much less efficient than the vehicle with a 84kWh batter and a 300 EPA range.