For me,it didn't hurt to have Diana Rigg in the film either.
But, he was the "rebound guy" after Sean Connery. I think anyone cast in the role would have been criticized. The series would have benefited in my opinion and not become so cartoonish if they'd stuck with George rather than going to Roger Moore.
Actually Lazenby was second choice----they wanted Timothy Dalton but Dalton refused saying he was too young (he later made another Bond).
Yummy Dalton.
Lazenby went to the audition satorially correct---dressed as Bond, even down to the Rolex.
But when he accidentally punched out an actor in the audition---the Bond producers were convinced the male model was aggressive enough to play Bond.