Same thing is happening here. The helicopters made the game easier. Helicopters keep crashing into each other & blowing up their own tanks. The more helicopters & tanks they lose, they double-down & send even more in, destroying more of themselves in friendly fire.
I do realize this makes it a highly accurate simulation of Russia's battle competency though.
I think the helicopters & pickle jars come into the game too early, maybe don't send the first helicopter until the player gets 10 tanks? Maybe cap the number of hearts & tanks on the field at once? My machine slows down to 1 FPS once there's too many hearts.
(Love the game though! The pre-helicopter version had a Flappy Bird feel, bite-sized game length & even 8 tanks felt like a high score!)