The game is unplayable because there is not enough gold mid-game. This always used to be a problem but since you updated the system we cannot easily put rare and common gold production on our heroes. My next promotion required 2027cc but I only generate 104cc every six hours. So it is 5 days just for the I highlighted tech. (it is longer if you include radar HQ and Meger barracks) .
This is at level Lv61 and the problem worsens as you progress to Lv100. Worse still at Lv81 you must research all three branches (army navy and air force) together.
If you notice the hero list from my main account I have Level 3 rare and common gold production on all my spare heroes.
Solution - revert the change so we can again open the first two hero skill slots with just EXP