What am I doing wrong? o .o

I love (boomer mostly), barbarian, lancer, and knight, yet can't seem to find a build to use in all areas; U6 farming and shadow towers. It seems that it's kinda mandatory to either switch classes or switch gear when going from u6 to ST.

I'm currently power level 2004, mastery level 160, and if I take my pure magic find build into a ST, I get destroyed very quickly as boomer. So I switch my MF stats to pure damage, use rapt berserker and attempt to kill things fast enough to heal with the ally heal... Not even close.... Then I go into desperate mode, using as much %max hp as possible, try st with 90k hp, use prowling shadow ally for heals, and STILL get destroyed quickly. Mostly when the mass of mobs surround me.

My friend says I'm playing the DPS class wrong, like a tank, that I should kite more and stay away from big mobs during ST. But with the amount of times that groups of ST mobs come after me, if I were to kite every time, it feels like it would be a nuisance for other players having to chase the enemies.

Anyone have advice for boomer? possibly lancer/barbarian/knight.
Hat: MH/AS/MF/CD
Face: MH/CD/%MH/AS
Melee: PD/CD/Jump/AS All radiant
Spear: PD/CD/Jump/ER
Ring: S4 - PD/MF
Ring: S4 - PD/ER
Emblem1: Surestrike
Emblem2: Martial