Well... it would have been better because we wouldn't have James' asinine sacrifice scene. But still bad.
And James couldn't have really known anything about Enclave. My impression was that the only people who knew anything about them were the Brotherhood and the guy in Greyditch (or whatever the place with the fire ants is called) who went east to get away from them. Until Autumn came to the purifier, their presence in the wasteland was limited to eyebots, and most people thought they were just playing some pre-recorded message. There were some files on the overseer's computer indicating that they made contact with Vault 101, but I can't remember whether it was before or after James left.
Either way, he had no reason to think they were a threat greater than any other faction (other than Autumn shooting the scientist because Bethesda's writing). And what army did he plan to use to defend Project Purity, since the player only goes to the Brotherhood for help after James is already dead?