"Starship class" is set dressing. It's never been said in such a way as to mean class and not type. "Constitution-class" is canonical, not necessarily the original intent of Matt Jefferies, but so what? It's not like they stole his work. He got paid and frankly, I don't think he much would have cared if they kept his scribbled-in-margins notes about "17th cruiser type" etc.
I'm not sure how this has become the big deal it has.