Right now, I kinda feel like international trade routes are way better than domestic trade routes. The main reason for this is that international trade routes give gold which is often a better resource to have than food or production that you get from domestic routes. Gold is not just useful for maintenance costs but also very useful for rush buying pretty much anything, including units, buildings, and even districts with Reyna. This will far outweigh the small amount of food or production from a domestic route. Now, I know there are policy cards that buff domestic routes but I still find that international trade routes are often better. The only time I use domestic routes are in the early game when I don't have a good international trade route yet and I want to help a new city grow. But after that, I tend to focus all my trade routes to other civs. You can get some insane gold from international trade routes especially in the late game!! In my first GS as the Maori, I had like 17 international trade routes and I was bringing in around 500 gold per turn. At one point, I had over 10,000 gold!! I could easily rush buy anything I wanted. There was no point in using domestic trade routes or even caring about production. And of course, GS buffed sea based routes which makes international trade routes even better.