Completely correct.  Anyone who thinks the rental value of one farm has anything to do with establishing the value of another one hasn't thought about it very much. 

The rental value is determined by how much you can pay and still consider it to be worth farming.  This is going to be more on higher yielding land, less on lower yielding land.  It will be more on easier farming soil or shapes, less on harder farming soil or shapes.  For a given operator, it will be more closer to base, less farther from his base.  None of this is rocket science.