Why it's always a good idea to max out your air defenses

Most of the times, you may encounter an all-dragon raid, balloonion, or GiantHealer. Now, the thing is, the air defenses could have gotten those air units faster- why didn't it? The answer is that the air defense isn't strong enough. Most people don't realize this, but Maxing out your air defense- or at least, equaling the level to mortars- would make everything harder to happen. For instance, level 5 mortars with level 3 air defenses would succeed in a ground attack- but they would fail against air attacks. But the opposite would also be true. So, what is the solution? Simple. Equalize your air defenses and mortars.