Ok so I am getting absolutely owned on this quest. I get to Black Mountain and about ten super mutant masters attack me. I'm at level 22 and there is no conceivable way of getting past all of these mutants. I've read elsewhere that being a level 22 should make it decently easy to get this quest completed, but I don't see how it is possible. Am I doing something wrong? How the hell am I supposed to kill of these things? I'm traveling with Ed-E and Cass too. It is just not a fair fight, and I really want that power armor.

I'm playing on PS3

I'm playing on PC, but I don't think it makes much difference.

Got to the top of the mountain at lvl21, with Boone and ED-E as companions.
You should sneak all the way, (Silent Running helps a lot) that way you can engage
1-2 enemies at a time. I used the Anti-Materiel Rifle (Sniper Rifle is OK too I guess) to
one-shot the Masters, they never even hit me. Nightkin will surprise you sometimes,
but with ED-E's sensors you can use VATS even when they are using Stealthboys.
If you got help from Neil (50 speech) 3 Nightkin will attack you at the top, any weapon
with high DAM and/or armor piercing ammo should do the trick. I recommend to follow
the road, but there is a shortcut too. (be sure to dodge the huge-ass boulder if you go that way)
There is some radiation too, pack some Rad-X and RadAway.

Hope this helps
Quaternion

High DPS weapons for the most part. Only a few of them have armor. Move slowly, you shouldn't have to fight 10 at once at any point. Two to three.

I know exactly what you're doing wrong, you're fast travelling to the top of Black Mountain. When you do this on that particular quest, every mutant on the mountain is waiting there for you. Instead, take your time and walk up from the bottom and fight them one or two at a time. This works a lot better.

Do you need to get there for "Eyesight to the Blind"?

There is a simple way that you don't have to face any of the mutants. Go through Scorpion Gulch. Scorpion Gulch is accessible thru Hidden Valley (Brotherhood of Steel). You might have been there if you have done the BoS quests about retrieving the holotapes.

If you are approaching the radiation crater from Hidden Valley, go to the right of the crate to get on a ledge. Work along the edge to access the top of the BlackMountain. Your companions may run off on you but you will mysteriously see them again at the top. The backdoor gate is a Hard lock so you may not be able to do it if your lockpick is less than 75. Once you get in, you will find your companions fighting 4 Nightkins. Help them out before going into the buildings.

Unless you want to fight more mutants, do not go down the hill using the road. There are 2+ mutants near the fallen satellite dish. Big mess and the game was frozen on me when I was about to get them all.