Well depends on how far into the Fallout Universe lore you go, in 2242 The Enclave basically get's their teeth kicked in, and even before that, the Brotherhood isn't the power they once were because of encounters with the Enclave. And then any time after that the Brotherhood gets much weaker by being stupid and going against NCR. I do understand the idea behind not using the 'big guys' Suppose the Children, Regulators, Rangers, New Reno families. Not a bad list.