Before you read this, know that you're not supposed to be able to win the game entirely in Dragon form.
I don't agree that 9 total skills is all you should be able to research. The system is already in place to say you can bring 9 and only 9 abilities to a round. What's the difference between that and forgetting an upgrade if you have 9 researched except to be more inconvenient?
Given the mobility of the Dragon, I think your hypothetical example giving it the power to take out the expensive Juggernauts in a few seconds is giving far too much power to the Dragon. Even if the Dragon didn't survive the attack, it would still win because respawning the Dragon is by far cheaper and faster than replacing the Juggernaut is for the enemy.
I do think that the Dragon in its current form in Campaign mode is really too weak and needs the equivalent of 30% Damage Reduction as a base ability, not a researchable and equippable skill.
