There IS the issue that if the dragon dies early on then the rest of his units/buildings are at great risk, but that could be where the anti air being a little more effective would come into play. If the missiles traveled a little faster and the jet pack had a slight cool down before it starts to recharge again. Though perhaps just a cool down upon depletion might be a good idea. After I left for work from posting this I did think about the possibility of maybe a 3 second cool down if you run out of charge? Definitely would discourage people from just mashing the right click so much and becoming nearly untouchable.
As things stand at this moment you could have almost as many hunters and grenadiers as you want but you are barely going to scratch a jet-pack-spamming dragon. If you are a good aim, you could easily kill another dragon with any other dragon but that shouldn't be the only sure-way to do it.
also, another idea.
For machinima purposes: I notice that while in dragon form the mouse wheel does not have a function. how about when in dragon form you could use that to rotate the camera around the dragon, let go and it snaps back to normal. If someone wanted to make a fan-made trailer that would help quite a bit. Also good for tutorials. things like that.
Also, Stabbey, I do recall that you mentioned some re balancing that could be made, I do believe that extending the time it takes until you can summon the dragon would be a good idea. Maybe add a few more minutes, let both players build up their defenses and armies before the dragons roll out. In the pvp matches I have done, I was in the lead until his dragon appeared, then i was focusing on killing his dragon (over and over again!) and was just trying to defend what units I had left.
(ALL of these criticisms are coming from one who seen the trailers and thought "You can play as a dragon?! I'm getting it!" I would REALLY like to see a game where you can play as a dragon and have it do well. But I want the dragon to be "fair" and not an annoyance to fight against.)