I have an anecdote. Bear with me.
A little while ago, I was doing vocals in a black metal parody band called 'The Spire of Inversion' (named for one of the 101 rules of black metal). We didn't last very long, but I wrote lyrics about all the various BM cliches - demons, worshipping Satanic monoliths, etc. etc.
None of them were very good, but my epic was going to be about being sodomised by Satan on God's throne in Heaven, which is an idea I'm proud of.
The reason why I mention it is because no matter how preposterous my concepts were, Scandanavians of various sorts had been there before me. And they meant it. Let's not forget that Varg's first band was named after Tolkein's Orcs.
That's the peculiar genius of Brandon Small. His songs don't seem like jokes, because bands that had come before him have done things that are far, far more idiotic (I'm looking at you, Cannibal Corpse). But then you realise that he's singing about mutating into mermen and overthrowing the land-folk, or summoning monsters in order to gather testicles for some evil ritual. Or something.
If people didn't know it was a joke, they'd probably take it seriously. And, that, my friends, is satire.