Umm...what? Let me think: warp drive, phasers, communicators, transporters and some new tech like the Genesis device. Were there some faxes or chemical powered rockets I'm not remembering? Really, I'm drawing a blank here—what "huge technological downgrade" are you talking about? Kirk's print book and spectacles? (The glasses were explained due to Kirk's allergy to retinox.) Was there the squeal of a 1400 baud modem from Uhura's comm station? Wooden wagon wheels on the Enterprise? Solutrean spear points on the photon torpedoes?
Meyer wanted Hornblower in space, not Rodenberry's world where the sonic showers materialize clothes onto you, where everything was automated. In STII they were almost manually loading photon torpedoes, picking up grates and preparing the launchers. Why? To evoke preparing cannons on a sail ship. In fact, the idea of photon torpedoes as physical missiles is a rewrite/downgrade - The Making of Star Trek
describes them as:
Energy pods of matter and antimatter contained and temporarily separated in a magno-photon forcefield.
There are no missile storage areas in the original 1975 Enterprise blueprints, just photon torpedo generators. In STVI they were cooking food in a kitchen, a world away from the replicator-like food slots of the original and animated shows.
They wore heavy jackets on away missions - what about the temperature-changing smart uniforms of TOS? Buttons on the turbolift in place of voice commands? WoK's infamously bulky flip-lid communicator? The Enterprise interiors were more cramped, we never saw the wide open cargo deck or rec room again.
There's no doubt that Nicholas Meyer and co. reimagined the Trekverse. It was more militant, it was more relatable to the 80's, technology was less pervasive in everyday life.