Most people think like that, and in some ways there right, but lets look at it in another way.
instead of mating a collie to a greyhound, the greyhound only realy adding speed to the mix, its certainly not adding staminar ,
so lets look at the lurcher, the lurcher allready has staminar , good feet , good coat , intelegence , and probly generation after genration of worker.
so you have all the good points from the collie, and all the good points from the lurcher, but NONE of the bad things from the greyhound,
its like having the staminar double bred in to the dog.