The individual developers, including lower-grade writers, do what they're told by the senior people. That's the way that companies work. There were also indications at one point after the ME3 debacle went public that those senior people were NOT interested in input from "the team", and that it was a top-down management/design style.
The indications were related to the ME3 ending where it was just Hudson and Walters making all the decisions, I've read quite a bit on the subject from Bioware writers themselves and the way they write stories is that each writer has his own segment that he or she creates it and then they talk with all the other writers ( which didn't happen for the ending ) and make changes, and improve it overall through that.
So I hold all the writers accountable for the shitty state of their games, not for everything story wise because there were choices made that they were forced to accept ( The Qunari, Orsino boss fight if you side with mages and so on ), but for the most part it was they as a team who decided what to do story wise and they fucked up.
There're things that I do blame the junior staff for, including unprofessional comments in BSN, but the games themselves are the fault of the senior designers and the management.
Considering what I just said above that is true for the ME3 ending, and perhaps the whole art choices and gameplay choices ( and I say perhaps ) but it does not apply for most of the writing.