maybe its just because im using a barbarian with Critical hit and ancestral call and I can basically kill a boss before he can do much damage to me. Like Vanarhost, he's gone in like 2 hits when I go through on Champion difficulty
Maybe you need better armor on or up your health regen so it regenerates faster
YouTube - Champions Of Norrath: Kathauun Arena Battle
Theres a video I made of me playing champions, thats how easy most of the bosses are for me. Just get alot of regen stones, upe them even and put health regen on all your armor and your helath usualy goes up faster then they can take it down