It seems like there is room for something in the middle here. I took a look online and found: IOF's and Corporate Businesses. On a Low Pop/Non Ind high tech world, the higher tech could cause the lower population to act like an Ag world, with most, if not all, of the population working for the IOF or CB that owns the farms on the world.
Traveller doesn't have a system for this to work, so it would be something like a house rule. I remember a scene in one of the Star Wars novels, where someone was on a Agri-world with many fields being harvested by robot harvester machines. Hadn't really thought about it until now, about how something might be possible or necessary, like in a Traveller setting.
Going the other way, how much population would a low tech world need to have a viable off world agricultural presence, if they were part of an interstellar trading route?