"Perhaps there exists an alternate transporting system for long, low items such as these pallets. Say, the corridors in TOS are very high, with lots of empty space atop the heads of our characters. There might be futuristic invisible trunkage up there: not just dataways or magic power flows, but a gravitic tube-mail sans the tube... Doesn't explain the arrangements of the TOS movies or the TNG era, though."
The overhead space of the TOS ship's coridors has many hurdles in the way.
Besides, I think what we're actually looking at is a holographic illusion that creates psychological space that actually isn't there (holograhic technology was already a concept for TOS that didn't make it until TAS' "holodeck").
I know it's a rather unorthodox but inevitable idea if you want to confine these corridors / deck height plausibly within the given space of the Enterprise,
(A pet theory of mine is that Kirk is actually explaining this to Ambassador Sarek as he takes him to Engineering in "Journey to Babel". I would find it hard to believe he's just saying "notice our efficient GNDNs overhead"
I also think that both the running around in "Let That Be Your Last Battlefield" and ST II clearly indicate that all decks are physically connected by stairways to one another if the tubo lift system is inoperate. And you'd need to have such a traditional system if you need to bring bulky equipment from the freight storage below in the engineering hull to the upper saucer section.