Those are fair arguments.

I still feel the Brotherhood in the west should be all but dead, but that's just me. From what we know, the western Brotherhood was almost completely wiped out by the NCR. Those that survived went into hiding, like we see in Fallout: New Vegas with the Mojave Chapter. With most of their members wiped out during the wars against the NCR and Enclave, these surviving chapters are probably going to be hard to come by, and their numbers few. The Mojave Chapter hardly had enough people to go out scavenging, let alone wage war against anyone. Surviving chapters would have to live in hiding, and I don't think that can be achieved with numbers high enough to wage war.

We know there are chapters of the Brotherhood of Steel that thrive, like the Eastern Brotherhood and the Midwest chapter, but those are cut-off from the west, and in some cases completely opposed to its original ideologies. Not to mention it's not likely they would show up in Washington.

It's up to you though. I am not demanding anything. And if you say you're keeping the Brotherhood in, that's fine with me. I just personally don't think they could still be around in great numbers considering the NCR almost wiped them out, and continues to hunt them down wherever they poke their head out.

EDIT: Another thing. If these Brotherhood guys are keen to the original ideologies of the Brotherhood of Maxson, then they are opposed to recruiting wastelanders. This means members must be born into the chapter. This makes it even less likely they'd survive, since they would have no means of recuperating after heavy losses.