Local map apps would probably fare much better. Can't speak for Greece, but I've had a really analogous experience in Czech Republic - as a city dweller, I've

Local map apps would probably fare much better. Can't speak for Greece, but I've had a really analogous experience in Czech Republic - as a city dweller, I've used Google Maps for all sorts of things around Prague without issue. Once you move past the Central Bohemia region, however, the data gets just as spotty and unreliable as you described. Mapy.cz saved my ass and has impressive detail even in quite rural areas (then again, OpenStreetMap is frequently much better than Google Maps as well.)