The main point is "some". Believe me such fiends not extremly rare but much more often you'll get weaker one even with tragic prefered. More than that fiend is the only way how a bard should kill solo. Bards can't permalag you thus the only reason you die to them is your greed to seal the kill and staying too long:) Try to fight people with resist mental up with bard(even cloud/fire giants) believe me it's way different. And there is an edge that would help you vs fiend if you care. At least I believe this edge do this though haven't tasted it myself.