What do you think on the lack of pure Flying-type Pokémon? Is it a bad thing or a good thing?
Ironically the lack of pure Flying-type contrasts how Flying-type is paired up with other 17 types, what do you think about this?
I'm going to answer both topics at once, as they're very close to each other. Flying is kinda like a side type, Pokémon are always something/flying, until Tornadus came to existence to break the rule. While a side type, it doesn't make it less important, not at all, and that's what makes the flying type so unique: its versatility.
In the first generation it has been decided bird Pokémon should be normal/flying instead of just flying. While they lose fighting resistance to this, I actually like they did this. As Hikari just mentioned above, a pure flying type should be an embodiment of the wind, like Tornadus, or something like in the image in the spoiler.