I'm once again going with the fact that a guy who lived in a vault for all his life came out and handled this place pretty nicely so a highly trained militant group should do just as well if not better.
Ever supposing they have the armour, so what? You see lots of Brotherhood members KIA. That and they are dropped on the world, which means to get the power armour their have to befriend the brotherhood. Even supposing they scavenge armour they won't know how to wear it until taught.
IMO they can survive up until they come across the Enclave, then they die.
I'd prefer to word it; It's full of people assuming things based on reletive feats and comparitives.
Saying they can learn to wear power armour easily/quickly because the Lone Wanderer can is just.... assumputious. There's no logical reasoning behind that.
Maybe they are, but since they are trained soldiers i'd rate them as i would veteran BoS. They wouldn't likely die to anything less than a large groups of Super mutants, those giant super mutants, or the Enclave.
Super Mutant physical strength is only alluded to, we do know they can easily tear through Power Armor with their bare hands, which can take 2,500 joules of kinetic energy/force without being damage (Not sure exactly how strong that is).
Mmmm, basically a gun would hit on area for about 9k joules. But that' because it's small.
In theory the armour would be very strong against something that hit a large part of it over a small part, due to penetration factor, i.e why the tips of the bulelts have an edge.
If we're guessing for examples sake a Mutant ripped his arm off with the suit working then you're talking about allot of pressure, i'd guess at around 7-8 times stronger than a normal person.
If he literally thore through the armour probably allot stronger still.