Total grinder. If it takes 1 hour to get every unit in your army to level1, it will take 2 hours to get your army to level2. 4 hours to level3. 8 hours to level4. 16 hours to level5. 32 hours to level6. 64 hours to level7. You level up quickly at first, but exponential growth eventuwlly bogs you down. And then, hey, if you pay real money, you can buy your way around the slog they built into the game. Which is the whole point.