i made 100 pvp with my dragons never losed one
drgons are not made for be launched in middle of 20 melee unit, but to harass with fireball and defend your shooter units if someone try to reach it for example with cavalry.
if you send a dragon to charge is obvious that his entire army gonna focus on it and he not last much.
consider dragon lev 20 matters nothing maybe you skilled it very very bad.
you need to max his hp regen and health point first
but yes they need to put back old resistance wich where higher like 40-40-80