This indicates that automated interstellar vehicles are employed in the TOS era to convey needed raw materials
...Something we subsequently see in TAS. Which raises the question of whether the fully automatic Delta Vega station in "Where No Man" was visited by manned or robotic "ore ships" every two decades. Possibly the former, considering the station had facilities for people - including a brig, something one would not expect a random ship to need unless she regularly shipped a sizable crew capable of getting into trouble all on their own.
The bigger question is, why would anybody want to haul ore? Ore is precious materials plus worthless dirt - why not separate the dirt first and then ship the materials? Hauling of ore suggests that the Federation (and its environs) features a lot of extremely simple or primitive mining communities or automated mines that lack refining capabilities and rely on centralized refineries. This further suggests that space travel is literally dirt cheap, or else it would make more sense to build a thousand refineries for a thousand mining planets than to build even a thousand ships to feed ore to a single refinery.
Or then these folks haul ore because it's less likely to be stolen by pirates. A centralized refinery can be defended against pirate attack; thousands of robotic shipments cannot.
Another name for a "transport"
Here I'd emphasize that the transport category can cover a lot of very different types of stuff-moving vessels. Supply ships deliver things where needed, on a schedule, to keep up a supply - which is very different from transporting materiel to a battlefield, or delivering goods to a purchaser, or hunting for profitable shipping deals in ports all around the galaxy, etc. Physically different vessels might be needed for the applications; historically, this has been the case.
Whether the Lantree possessed any ship-of-the-line qualities or capabilities remains debatable. Is an Oberth a ship-of-the-line, too? Is Kasidy's freighter one? Data explicitly belittled the armaments and defensive capabilities of the Lantree, suggesting either a strip-down after the TOS movie era, or then an upgrading of standards on what is battleworthy.
ships that carry non-time sensitive stuff on regular routes
One would assume these ships would be rather large, to compensate for their inflexibility and to lower overall costs. The Woden, in both her incarnations, was minuscule, despite hauling supposedly low-price-per-mass bulk. The ENT Class J cargo train was a more convincing ore carrier, but not automated - yet that may merely reflect the state of the art of that backward era, or the strategic situation, or both. I'd love to believe in vast automated carriers of ore and grain (the UFP has "farming worlds", apparently not for local sustenance, and used to face famines as per ST2), in addition to the midget cargo-movers seen so far - but this is the one field where speculation and noncanon material is all we have to go by.
During TOS "Friday's Child", Sulu commented that "the best a freighter could do is Warp 2"
Which is a whopper of a claim. Why aren't freighter operators interested in warp 7 ships? Are the obstacles technical (big engine like that -> no room for profitable cargo), political (Starfleet won't let civilians have big engines) or business-based (nobody can make profit on a fast starship which is expensive to operate, because nobody needs stuff delivered from star to star in less than a week)?
All the shows feature these tiny high-price-per-mass movers, some of which operate as tramps, hunting for profitable freight deals. DS9 suggests that even Kasidy Yates' ancient-looking tub is actually really, really fast, completing a circuit of several star systems in less than a day ("For the Cause"). Yet as late as the 2260s, freighters were categorically slow. One is tempted to believe in not just a combination of all the three excuses given above, but further a profound disinterest in doing business in space transportation!
Perhaps back then, the fear of Klingons had almost completely shut down interstellar commerce? That'd fit the fact that "Friday's Child" also mentioned convoy while all the rest of Trek showed individually traveling cargo movers, right until open war with Cardassians, Klingons and finally the Dominion.
Timo Saloniemi