Their reasoning seems a little unsound - if the Shadow Slayer is more powerful than a god in any real sense (and I thought most of it was to do with the sword) then it shouldn't be possible to capture them. Likewise, if they can be held captive or maimed by mere mortals, they're less powerful than you and drinking their essence makes no sense.
Cults? Having sound reasoning? It's not as likely as you think.
That's probably Phobos's blood in the last panel. Makes me wanna ask though. What color do Dryads bleed...?
I know the knee-jerk reaction would be green, but my actual thought-out answer would be yellow/transparent since I think the closest parallel would be sap.