Is breakthrough unbalanced?

How come in Breakthrough the teams seems so unbalanced with vehicles? The offensive teams get multiple tanks, a heli, ground vehicles and can push fully into the zone (this part I understand why). However the defensive side gets like 2 light vehicles & confined to the zone. It’s fun only for one side. I’m just looking for understanding maybe I’m missing something or do other people think it’s an unfair advantage. I like the mode in certain maps without tanks and helis when your just going back and forth trying to keep the other team out your zone but when the other teams pulls up with 3 tanks it’s like WTF.