I'm not sure what you did differently, but personally the first thing 'I' check is not 'how to do more damage' but 'how to avoid damage'.
Each Dragon usually has an elemental weakness. The opposite is usually their 'strenght' aka 'elemental based attack'.
So first things first, equip your party with rings or belts or craft armor with elemental resistances.
Next: Make sure your potions are full (Don't forget: Your party members may share the health potions, but the other slots you have to manually fill on for each character on the 'equip potions' table and refill each time after use at the table, by clicking at the potion).
Then: the weakness based weapons help.
Also, while each dragon tends to have a certain behaviour, it does not necessarily mean it always does the same. Sometimes they fly around more, sometimes they call for help more often (don't underestimate the little beasts the Hinterland dragon and some others get - better get rid of them ASAP).
Then: Your mages: Vivienne running at the dragons is ok as knight enchanter. All other mages wanting to get within cuddling distance is good for the dragon, bad for their health bar. Keep an eye on them.
If you aren't partly controlling them yourself, you might want to check their behaviour and change what spells they are most likely to use according to the opponent.
Also make sure they have staffs with the element of the enemies weakness equiped! That does wonders, especially for when they cast this barrier onto themselves.
And I guess this goes without saying, but... Do avoid the dragon attacks? Be it fire blast, tail swipe or whatever. Also running away from the dragon when he pulls you is also a good idea ;P
And skill points: Make sure you've spent them all.
If all doesn't help, you might be better off controlling Viviane, blasting the dragon appart with ice spells, setting ice mines and ice walls. Alternately, try a different group constellation?
What do you mean with enchanting?
If you are talking about pimping you current armor, you need to check for arm and leg guard equipment to enhance your current armor - if the current armor has slots for that. Self-crafted usually do.