To solve the problem for yourself, you can also long press a road you don't like and select Avoid Road.

> I wonder, how difficult is it to make minor edits to the map data?

The map data is OpenStreetMap, so you can make edits via the standard OSM methods:

Web: https://ideditor.com/

Local: https://josm.openstreetmap.de/

It's just OpenStreetMap, see https://wiki.openstreetmap.org/wiki/How_to_contribute