My first post on forums so go easy on me
So a LOT of this is going to be my own interpretation on Maxson, state of BoS and fate of Sarah Lyons based on Quinlan's logs in fallout 4, what we know from fallout 3 and some basic 1+1=2
My theory goes that after Broken steel, with the Enclave threat totally purged, and BoS in strong position, Owen Lyons power base started to crumble. The outcast sympathisers inside BoS started to plot for a hostile takeover but couldn't yet do anything, it was only after Owens death and Sarah becoming new elder that they made their move. First by assassinating Sarah in middle of mission, I'm backing up this point by notifying readers how well trained Sarah was, we can see it many times and it is even mentioned in Fallout 3, So it would be very strange for her to fall on a regular mission (note: it is never said that this was regular tough in fallout 4) and the timing of her death just adds suspicion. Next they start to look for a good candidate who could back their old west based ideals and find one in Arthur Maxson. Now lets talk about Arthur a little bit...what we know of him in fallout 4 is that he is supposed to be super-soldier by age of 12, even going so far as killing Deathclaw by himself in age of 13. Now here is the thing, the Arthur that i met in fallout 3 was stuttering slightly wimpy little kid, and still from 2 years onwards he was supposed to be turned into something rivaling Lone wanderer?....
No, what i think happened was that on those journey where Arthur made those first "heroic deeds" Lone Wandered was actually with him and he was the one that did all those things, but the new leads on BoS, the west sympathisers turned those to Arthur's victories so they could sway remaining BoS to their side, since many of them were still Lyons fans. Now you might ask " but NightSound, in fallout 4 Arthur clearly is really strong isn't he?" well he is..but is it by natural training? Proctor Quinlan writes that Arthur is "Assisted, even enhanced" and the way that Quinlan tries to hammer the point that he is still human makes me believe that BoS used some serious implants to make up Arthur's flaws, and really without them he would be pretty ordinary man if you even can consider him to be a man.
Now lets talk how the BoS acts in fallout 4 that I think supports this theory, and no not about how they hate synths and are really like west coast all over again on matters of tech before protecting people ...about the need overtly enforce this culture of tight brotherhood (no pun intented), no questioning orders and revering of the leader that are clearly much stronger than they were in times of Fallout 3 and maybe even stronger that what we even see from the Nevada branch of BoS. I'm pretty sure that this is because actions taken against Lyons and the need to ensure that that doesn't happen against Arthur and the powerbase that now controls east BoS from people who remember what east coast BoS was for a moment in leadership of Elder Lyons and his daughter.