I agree completely with KingDaniel
. It's silly to pretend that what we're seeing on the TV or movie screen is an exact, literal depiction of an actual future. All Trek productions are simulations of a hypothetical future made with present-day technology, executed by different creators and designers, etc. And so they're all going to differ in how they interpret that imaginary reality. Differences in set and technology design are no more "real" in universe than the change in Saavik's or Tora Ziyal's appearance and personality in consecutive appearances. They're just different artists' interpretations of the same conjectural thing.
Gene Roddenberry himself would have been the first to agree with this. In his preface to his ST:TMP novelization, he took on the voice of a 23rd-century producer who'd dramatized the "real" adventures of Kirk and crew, and he apologized for the exaggerations and inaccuracies in his fictionalized account. When Trek fans asked him why the Klingons had changed appearance in TMP, he told them that the Klingons had always looked that way, and TOS simply hadn't been able to depict them accurately. He never would've wanted the fans to take every last detail as immutable gospel. He wanted them to accept that what was onscreen was just the best approximation the producers had been able to manage, and was glad for the opportunity to replace an earlier, cruder approximation with a more sophisticated one.
If Roddenberry himself were still alive, if he had been the one in charge of rebooting TOS, he would've been just as open to a wholesale redesign of the sets, costumes, technology, etc. as J. J. Abrams was -- and he wouldn't have bothered to try to rationalize it as an alternate timeline, but would've just straight up changed things and told the fans "This is a truer version than what you saw before, so deal with it." In fact, that's essentially what he did in TMP -- made wholesale design changes without explanation and didn't feel he needed
to justify why a big-budget tentpole motion picture had more elaborate sets, costumes, and makeup designs than a low-budget '60s TV series. As a producer, he was no doubt constantly frustrated by the budgetary, technological, and logistical limitations that forced him to make compromises in his depiction of the future in TOS. He didn't worship every button and light as immutable truth the way many modern Trek-tech fans do; he settled for them as the best he could manage with the limited time and money and technology at his disposal. And when he had better resources, he gladly started from scratch and came up with something that he felt came closer to what he'd wanted in the first place.