I believe the Athlete-Model is perhaps more of a brand ambassador. Remember the lovely Marzocchi Girls? Men of the right age most certainly will. Don't remember if they rode bikes. Not at all. But I remember them and the brand.

A brand ambassador should represent your brand in a favourable light, be approachable and likeable.

The product being marketed is also a driver.

I would for instance be more interested in a DH bike that has won a WC race, regardless of the pilots lack of facial symmetry. Whereas I wouldn't buy sun glasses that were worn by an athlete that I did not admire aesthetically.

Some people will always need to represent the brands of any competitive sports product with results. If consumers wish to get faster, they buy the perceived faster kit.