Re: TOS-era Defiant-class Ships
Nothing in that article precludes the possibility that elements of the final Defiant design were not inspired either consciously or subconsciously from the Leif Ericson or its concept art, or a dozen other sources for that matter.
But you can see in the preliminary designs how the shapes started to evolve. The design didn't start as a stripped down form of the Leif. Each piece evolved independently and only came together as the Defiant.
Baby, you and me were never meant to be, just maybe think of me once in a while...