The amount of stuff that I can imagine that I want to be fan art could fill a forum in of itself. People make art of what they like and not just any old idea.
I imagine that their contributions are more technological than necessarily hull design. Making all ships similar makes a bit of sense to allow for ease of repair, especially towards the beginning, rather than having a Tellarite ship being sent back to Tellar to be fixed, etc.
I wouldn’t be so sure if that. If the federation ships only had earth influence they wouldn’t have a secondary hull! We can thank the Andorians, the only founding member other than humans without a “hat”(planet of hats tv tropes). I don’t think it would be fair if the nx class gets to be refit as a federation ship and not the ships form the other three powers as well. Starfleet likely came from a merger of Earth Starfleet with the Vulcan Andorran and tellarite equivalents as all the ships were merged into one STARFLEET. The curved nature of the Galaxy Class and especially the Intrepid and Soverign classes show their Vulcan influence. And since the Vulcan ships from Enterprise were very efficient I imagine they remained in starfleet for over a century. Also the Tellarite cruisers share a resemblance with the Defiant. They would not waste all those ships. I can see the resemblance between Starfleet ships and it’s main four progenitor fleets. Starfleet tends to reuse ships such as the Miranda Class for up to and in the Miranda classes case over 100 years so I’d imagine the D’kyr class would stick around in the federation starfleet and be refit and refit for just as long.