There are some things Hawks can do that they probably should not be able to do, such as spreading CoE, or flying across the planet in one turn, or carrying an entire Dragon Hoard. I agree that those aspects of Hawks need to be looked at, and probably blocked. If that's what you mean by overpowered, then I can accept that. However, it seems to me that you (and others) are saying that even without these factors Hawks have problems.
(Other than as just stated) I contend that Hawks are neither overpowered nor unbalanced because the reconnaissance ability offered by Hawks is similar to that offered by the other unit of its type (pure aerial reconnaissance), and available to everyone.
Hawks are balanced because of the fact that they are available to everyone. That's the most fundamental type of balance possible. As you pointed out, that doesn't guarantee an appropriate power level. I feel that it is still an important fact, to refute the notion that the reconnaissance ability of Hawks is unbalanced. If battlefield awareness is so powerful (I agree that it is), but everyone can get it, then I see no unbalance.
That hasn't been the primary focus of this thread, however. Since the original post, the claim has been that Hawk reconnaissance is overpowered - and I'm asking "Overpowered compared to what?". The closest thing to a Hawk in the game is a Floating Eye, which has superior reconnaissance potential. It is true that only the Amurites can get it early enough to compete with other civs Hawks, but it should be just as valid to compare them as it is to compare a unit available to everyone with a civ's unique version of that unit.
If the conclusion that Hawks are overpowered isn't being made by comparison to Floating Eyes, then how is it being determined? A unit can't be overpowered in a vacuum, it has to be more powerful than something else. Before you answer, consider that a Hawk is almost as expensive to build as a Warrior, but can't attack or defend, and still requires unit support. [sarcasm]Sounds underpowered to me, better buff Hawks.[/sarcasm] Comparing Hawks to units with vastly different functions is unlikely to yield meaningful resuts. So against what inferior-yet-comparable thing are Hawks being measured, that demonstrates that they are overpowered?