If you have the skill to take on a boss that takes 20 minutes of sustained fire to drop half his life, then take that skill and get better weapons. Better weapons will allow you to kill them in 10 minutes or less. If you're exaggerating, well it's all your perspective and your impatience would lead me to suggest playing something like Clash of Clans or maybe Candy Crush...
Look, I'm not the only one on here saying it. To get better gear you have to do these missions.
I understand the whole idea of grinding and working for good gear, I get it. But sitting there for 20 mins shooting one guy isn't entertaining to me. I could be doing something else story wise, advancing, progressing learning more about the destiny universe etc. But no, gotta sit here for 20 mins while me and 2 other people shoot at a guys face. Awesome.