A case in point would be Franz Joseph’s ship designs. Would Matt Jefferies have done what FJ did if he had been tasked to come up with other Starfleet designs. I don’t think anyone really knows the answer.
Nope, I don't think he would. I think Jeffries would have considered the 'Starship Class' as the pinnacle of Starfleet technology, and 'lesser' vessels would be designed based on their function, and would look little like a saucer and secondary hull. The ships might have nacelles, but that would be the only similar characteristic. He wouldn't be a 'kitbasher,' which was essentially what FJ did.