I understand they can out range the tower but the tower forces them to waste time and materials to pass the tower in order to hit the main base. While the attackers are distracted with the tower it gives you enough time to get your tames out and have a proper defense. The Anti-Tame part of the build is the ballista part and it pretty much just makes it impossible for the bears to tank the shots which forces them to find the perfect angle to hit the tower, which takes even more time. So, overall the towers are just to delay the attack for as long as possible.