Considering the rate at which the hero's level increases and the level reset (and consequently, stat reset) in later missions, the map size doesn't seem justified, in my opinion. There's no point in running around exploring the map. It would make sense to show the final point on the map and an approximate shortest path. By the time you reach it directly, your level will be around 30. Long wanderings are not good for campaigns, in my opinion. 2-8 weeks for a complete playthrough of such a map, visiting all the upgrade locations, would be just right.
Considering the rate at which the hero's level increases and the level reset (and consequently, stat reset) in later missions, the map size doesn't seem justified, in my opinion. There's no point in running around exploring the map. It would make sense to show the final point on the map and an approximate shortest path. By the time you reach it directly, your level will be around 30. Long wanderings are not good for campaigns, in my opinion. 2-8 weeks for a complete playthrough of such a map, visiting all the upgrade locations, would be just right.