Actually range flying is based on best L/D ratio, and that is an Alpha, not a speed. So it is independant of weight, altitude, etc.
Since most aircraft dont have Alpha indicators the only indication we have of the best L/D ratio Alpha is the IAS.
Secondly the lift and drag is a function of EAS, so in real life we have to make compromises. That is only the airframe.
When we add engine requirements, even more compromises.
Who said life is fair?