At the beginning of the war, the Giant Dragons held great advantage, possessing genuine semi-god warriors in their ranks, while us Druids could barely threaten them by relying on Forbidden Spells that came at a great cost.
However, in the later part of the war, the Elves once again saw a turn of the tide.
The reason was a Druid had learnt a new Transformation Arcane from the remains of the ancient beasts annihilated by the Giant Dragons.
By using this Arcane, Druids could transform into the shape of the ancient beasts and attain part of their strengths and skills.
Remember, although these ancient beasts have been exterminated by Giant Dragons, they were once a severe threat to them; many among them were semi-god level entities as well.