Not to mention I thought the source of alchemical power in the original series was a more interesting concept.

Yeah, the Brotherhood explanation is weak. Like a tea bag that you let steep for ten seconds. There's something there, but it doesn't really have a flavor. You're left asking "that's it? But how does that power alchemy?" I won't pretend the explanation in '03 was objectively good, but it was definitely strong. Like five tea bags steeping in a single cup for ten minutes. I like my tea strong, but I know not everyone does