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He won't be level 5-8. The thing is, the map is such that the Rogue has plenty of room to maneuver (monsters aren't clustered tightly around the treasures), and the Rogue will get bonuses from stealth. When clearing levels 3-4, this experience bonus is quite noticeable, and therefore the Rogue can level up very quickly and upgrade not only the scouting branch but also the combat branch.