Ok so I am trying to get to the top of Black Mountain for a quest and along the way I run into groups of 5+ Super Mutant Masters. Now the best weapon I have atm is the Q-35 Matter Modulator with Max Charged ammo and it takes at least 10 head shots with a few crits to kill one of them. By the time I manage to kill one the rest have killed me. I am lvl 22 atm.

Try to draw them out one by one...otherwise pay a visit to Hidden Valley

As an energy weapons user, they're much easier if you have a heavy weapon, like the gatling laser or plasma caster.

I was like lvl 10 when I went up black mountain the BoS was one of my first quest lines. I used the incerator on them it was grind but I got through it. Bring med-x, rad-x, radaway, stimpacks, and nuka.

Obsidian took away the leveled creature feature. So it's not like fallout3 where you can go anywhere and the monsters will be your level. Personally I think it's a good thing.

Try and sneak by them going around the right side of the mountain. For me they stopped attacking as a group once I got passed the fence around the radio station.