I can understand why you'd avoid customizing trees and cliffs but it's clear you can use custom water placement for the oceans and lakes. Why not rivers? You don't need every tributary but I feel like having huge swathes of land without rivers is boring. It can be as simple as just being shallow water tiles and when I selected the detailed version of the map I was disappointed to find they aren't there.

I hope you update the map to include rivers. Maybe some day it'll have cliffs to represent mountain ranges too.

There are some bigger rivers, but most rivers are simply too small even for the detailed map. Some of the major rivers should be there I believe though.