At TH6, I can see why you don't understand what's going on. Level 3 balloons are pretty useless at TH6, since you can't really use enough of them to take out a strong TH6 base, unless they left their Air Defense exposed. And you don't have minions yet. And you don't have enough slots in your spell factory to take out an Air Defense with lightning spells.
It'll start to make more sense when you get to TH7 and especially to TH8. A TH7 has two Air Defenses, 2 Air Bombs, and 1 Seeking Air Mine. Healers wouldn't last very long against that. Indeed, they didn't, before they made healers invisible to air traps.
TH8 is even worse. Three AD's, 4 air bombs, 2 seeking air mines. It's almost impossible to get healers to survive all the way to the core of a base. Healers were basically useless against a TH8, unless you were willing to use them only on the outer edges of a bases. Or if you used a lot of them.
So yeah, at TH6, I understand that healers might be frustrating. But when you get to TH7 and TH8, you will understand why they needed to be made invisible to air traps.
And just wait for TH9: a total of 4 seeking air mines, each a one-shot kill against a healer.
