Glass cannon: kill them before they kill you.
MoF bosses: You’re a glass cannon? Not anymore! Get your defenses like a tank and slap my face with your bare hands!
Imho this makes all chars looking for same stats in skills and gear, in fact almosy mandatory, leaving no place for different game archetypes.
Average gear and any correctly builded char should melt bosses 20 levels below. Any 55 lvl char should experience a difficult 55 level boss with all bells and whistles. Same for any 90/100 lvl char facing lvl 100 bosses.
What else is the purpose of looting, crafting, planning builds for?