Naturally, the argument can be made that that when the Federation was formed, Earth-based designs were chosen because Starfleet was Earth-based, and it then became a tradition that carried through into the 24th-Century. But since the Federation's founding, it could very well be that a number of technological improvements originated on worlds other than Earth (for all we know, the Warp 7 engine may have come from Vulcan or the TNG-style phaser array could have originated from Andoria).Enterprise presented the Starfleet esthetic as exclusively human. No visual characteristics of other races' ships carried over to the Federation ships of later years. They were just slightly different Earth ships. Magically, they were more advanced than aliens spacefaring for centuries.
But a very case was made in ENT that Humans did advance very quickly after developing warp drive--so much so that the Vulcans thought they were going way, way too fast:
"We had our wars, Admiral, just as Humans did. Our planet was devastated, our civilization nearly destroyed. Logic saved us. But it took almost fifteen hundred years for us to rebuild our world and travel to the stars. You humans did the same in less than a century. There are those on the High Command who wonder what Humans would achieve in the century to come--and they don't like the answer."
--Ambassador Soval to Admiral Maxwell Forrest.