As others have mentioned, a fire resist set really isn't needed for this. Wyrm shouldn't be in the air for more than 30 seconds or so, 45-50 absolute tops.
What we do is whittle it down to ~72% with regular melee/rngs/plds and then fire off a SC to push it under 70 and force it to fly. Then when it's flying just have your rngs and blms go balls to the wall to take it under 35-40 and make it land. Hate will most likely be on them but it shouldn't be too hard for plds to get hate back, or you can sleep it in case a fire blast/wing got off. With decent melees, rngs and blms the whole fight will take around 10 minutes.
XI Wiki


