Very well. Instead of time travel, why don't you say that prior to the mid-2240s to early-2260s when things began to change, Humans had been the dominant species determining the "look" of Starfleet ships, from their external design features to their interior aesthetics. Hence why we get so many early ships following the NX-01 or Kelvinverse design trend, with some outliers like the Daedalus Class or the U/SS Bonaventure from TAS.
But beginning in the 2240s with the Constitution Class, as more species joined the fleet and the existing founding and early members of the Federation began to assert more of a role in starship design, the ships began to follow a less ethnocentric design ethic and started to feature more smooth, simplified, spartan features that weren't recognizably native to any particular culture but were instead born of a union of all the cultures involved. Previously externally carried technology was moved under the skin of the ship to not only protect it from harm but also to make it less recognizable as being the product of any particular species.
Starship design became less of a Human-dominated project and more of a collaborative effort between species, much like the Federation itself.