Anty-air units don't work against Dragon. Rockets are too slow to hurt the dragon, they can reach him only when he fight with another dragon. Only Imps fighters can fast take down enemy dragon, but Dragon may at any time morph out and avoid dmg. Dragons too easily do destruction greater than their cost, The dragon with the right skills can easily destroy units with a value greater than 60.
Solution: Increase the speed of missile and block the dragon morph for 10 seconds, after taking damage, and set 2s cooldown on dodge, and increase dragon cost and respawn time after dragon dead.
The dragon is a very powerful unit and should therefore be used with prudence.
I apologize in advance for mistakes, English is not my native language. I thought that this section will be adequate (There is no the separate space for discussion on balance, if a post is in the wrong place, please move it)