Sure, but should the lore suffer for it? And shouldn't the gameplay portray what the lore has stated?
The lore is after all the canon material.
Myron survived several stab wounds and gunshots in Fallout 2, yet in the end he dies from a stabwound in Reno in one of the ending sliders.
We have nothing on MWBOS apart from a minor reference in Fallout 3 and Tactics, and seeing as how Legion Centurions is decorated with power armor pieces I'd say they aren't doing too well to lose to Legion.
So saying they are improving? There's as far as I know no evidence of that.
If anything, Legion's centurions are evidence against it. Though they "could" just have fought a third faction unnamed to us that used power armors, but that's a bit of a stretch IMO.
And Lyons Brotherhood (Not CWBOS, they are hardly bOS anymore.) could barely do anything at all prior to the Lone Wanderers help.
Now think about it, Talon Company wants to sabotage the Capital Wasteland and now LB because of the water purifier.
They still have super mutants to deal with as they have not destroyed Vault 87 yet.
They have raiders now equipped with Enclave gear to worry about.
They have Ashur who's likely going to be pretty damn pissed at them.
They have enclave remnants left to fight.
And Crawler and Raven Rock filled with good stuff for them to use they destroyed not to mention that the Outcasts are probably going to be furious to their disregard of tech.
So how exactly are Lyons Brotherhood going to progress? They've made too many enemies, they could hardly stand against the super mutants and raiders, now they have even more enemies and only slightly better tech.
They won the fight against the Enclave, but now LB is weakened, and their number of enemies has increased.
And remember, quanity>quality if the quanity is big enough. (Helios One)
So eventually Lyons Brotherhood will either die or be forced to leave. (That's how I predict it at least.)