Yeah , you are right.
One top file (you can see in my top comment) I was making around during 5-6 days or 1 week. And this is only road surface.
It's very long work and very bored work. It's huge capacity of work in Photoshop.
You should always work with the grid, drawing the correct circles for different angles in isometric, pixel by pixel.
Lots of math and geometry calculations and don't forget that this is still in isometric.
The new teammate who will work with that stuff is good because other developers will be free for another things what they do.