If I were to rely only on my experience, I would say that, for the same computer (pretty old, 2010 "averagely powerful"), Old World is off. I played the game maybe an hour, and it was terrible, especially compared to Civ6. When I had to set Old World graphics on the lowest, it was uglier than a Playstation 2 game, and not only that, but it ran like crap. I had to wait sometimes 30 seconds, which is pretty long, to wait my scouts uncover the fog of war, and that was without the animations and all the hideout effects... I don't know where all the power goes in that game really, Civ6 has 10000 times the beauty/performance ratio. (wonder construction, day and night, smooth animations, etc... incredible compared to Old World) So maybe I'm wondering, if your sources are exact, if the lack of compliance to the average computer market is not what cripples the game popularity. (at least if it was impressive it could stir up some more interest)
It's too bad because I have a feeling that Old World would better suit my liking than Civ6.