Well, the lesson I've learned so far is that my build seems to be absolutely awful.
I teamed with another dragon to take out Thistleface, and they did most of the damage. Even my Gold Rage seemed to be a slap on the wrist compared to theirs. Then I went after Lorgus (Fire beetle for the Helian side), and died when Lorgus was at about half health. I've spotted flaws in my tactics, but those changes aren't likely to solve the issue completely.