The Star Trek Original Universe was fantastic for many reasons, but not the least of them was an effort at stylistic consistency with the ships over the fifty years of production. A knowledgeable fan could look at a Federation starship and be able to tell you, within a handful of decades at worst, about when the ship class had been designed and first built over the two hundred year history of Starfleet . . . or pick out when something just doesn't look right.
Such stylistic consistency is not something you just accidentally happen upon.