User blog comment:NaiflidG/Relating to Alastair in "On the Head of a Pin" and "Caged Heat"/@comment-104.167.139.175-20141120171010/@comment-11331875-20141120233109

That's true, anon -- there's quite the vast power difference between, say, Ruby and Abaddon, after all, and they're both black-eyed demons. And while it wasn't explicitly stated, one could reasonably think that Lilith was more powerful than Alastair, given the wild difference in how vulnerable each white-eyed demon was to Sam's demonic powers at around the same time. (There was only two episodes between Sam's powers killing Alastair and Sam's powers... completely failing to do anything to Lilith.) It is certainly possible that Azazel was stronger than Alastair, which, as you said, would be supported by the difference in their respective reactions to holy water. (I theorized why Alastair might ordinarily be immune, but that is rampant speculation not supported by evidence, so it is simpler to just go by on-screen evidence.) I'm still curious about the exact power dynamics and interrelations between Alastair, Azazel, and Lilith -- not to mention their followers, e.g. Meg and Ruby. I guess we'll never know for sure, though...