"Ya but the first hit wasn't roost and it still did only about a quarter damage..."
I wrote that on mine sorry. ^ That's the reason, unless i'm mistaken about something, those hits should've done more than half damage.
I ran this through a damage calculator. With my swampert with 269 sp.atk, it would at least do 224 damage to your dragonite IF it has MAX sp.def. So nonetheless, it should do more than the mere 100 damage I'm currently doing.