Well, by that logic, what town would be it's current size without the resort?
Routt County had half the population that Steamboat currently does in 1960 prior to the development of the resort. That being said, the vast majority of population lived in Steamboat. And Steamboat was the economic center of Routt County, the county seat, and would have remained so without the resort.
In many ways, Bozeman and Steamboat are similar. They both are historic towns that served as hubs for regional agriculture. Bozeman has developed more of an urban center with greater diversity of economic activity, likely as a result of the presence of a major univeristy. Steamboat became a resort.
Bozeman is the new Durango or Boulder. We'll see how long it stays the way it is.