Thank you for the great feedback!
I agree that most games end with building fighter jets and speeding across the map, and the more powerful tanks are rarely used. I have been thinking about how best to rebalance things without slowing gameplay down too much.
I really love the hot air balloon idea!! Just thinking out loud: Maybe replacing or nerfing the fast planes and adding a cheaper hot air balloon that is buildable earlier in the game can speed up the early exploration phase and make things more dynamic. Military hot air balloon combat also fits right into the slightly whimsical aesthetic of the game. I will definitely experiment with this!