Valid point. I think the tech that gives the harbor is called Celestial Navigation and is likely to be a medieval or renaissance era tech, which means it's a good way into the tech tree. We know there's also a tech that requires 2 galleys as it's eureka, which is also an early tech according to what was said in one of the first videos.
Celestial Navigation is a classical tech. In history it's been in use since Antiquity, and if you take any ques from Civ5, the techs go;
Ancient - Sailing (workboat, trireme, fish nets)
Classical - Optics (Lighthouse, Great Lighthouse, Disembark)
Medieval - Compass (Galleas, Harbor, +1 trade route)
Yet, if you take ques from civ4 then it goes
Ancient - Fishing (Fishing boats)
Ancient - Sailing (Lighthouse, GL, Trireme)
Classical - Compass (Harbor)
So all that's really happening is that the Lighthouse and Harbor are swapping spots in the tech tree (since lighthouses are built in harbor districts) and I imagine civ6 goes;
Ancient - Sailing
Ancient/Classical - Celestial Navigation (harbor district)
Classical - Naval Tech (lighthouse, GL)