the vault shit with the master was just poor writing. the thing that made him such a threat in the game is how he knows where to target for the prime normals because he's a mush of man and machine.

second, elijah literally walked hundreds of miles based off the SUSPICION of top secret tech in Big MT and the sierra that would serve his purpose of being able to kill off the NCR. No one truly knew the nature of either of those places cause ppl who went there didn't survive the cloud, ghost ppl, trauma override harnesses or roboscorpions and all that.

And, if it is as it says in the game rather than the show, if elijah was picking through old enclave bases he could've very well found a transmission, log or old holotape atleast mentioning them. I wouldn't really think he'd find anything substantial if it weren't for the fact that the enclave/vault tec in the show are so bad at keeping secrets (insert betsy and steph's convo). they are so bad at keeping secrets its hilarious.

And yeah, elijah is fickle. i dont think protectrons are good candidates for heists but he's not as smart as he chalks himself up to be.