Why are guns so much weaker than melee?

My previous two playthroughs were blunt melee and cool throwing, both with berserk. My current playthrough is reflex SMG with sandevistan, and while its fun for mowing down dozens of goons, bossfights and high health enemies are 10x as hard. Maxtac, Kurt Hansen, these are foes that die in 30 seconds to a melee build. I had to pump like 800 bullets into Hansen to kill him over 3 minutes. Why the discrepancy?