Hm... I see your point, and yet... it'll become easier to use up stamina. Right now you level up a lot more which restores stamina and exploration points. Right now you do low-cost main mission maps which give good experience per stamina. Eventually you'll be doing 3-4 80-stamina event maps at a time and then be done for at least 6 hours, and they don't give great exp per stamina, so you won't be leveling up every time you play.