Dethklok was meant to start the metalocalypse not stop it.

I don't know. I could never make any sense out of the convoluted under arc of this show. I've watched the whole thing dozens of times over the years and I still can't make a single lick of sense of any of it. There's no real continuity and as you said, plenty of contradictions. Despite what the creators have said about having a clear vision for the show from the beginning, it seems pretty clear to me they're making this crap up as they go along. I don't watch the show for the Metalocalypse.

"I said no camels, that's five camels, can't you count?"

Yeah, the finale made no sense if you look at past episodes, and pulled a retcon with so much stuff in the series..

I mean, what about crap like the demons from the church of satan, much less the blues devil..

None of it makes any sense like most people figured, heh..

What you all say is true. But the entire tone of the show seems to have changed over the last few seasons. The graphic violence is toned down and the guys in the band are nicer, at least they're less mean. Nathan practically acts like a concerned dad to Toki.
So this whole plot about them being the chosen ones might not make sense in terms of the way the show was set up in the beginning. But it does jive with what the show and deathclock have turned into in recent seasons.

"Apocalypse" doesn't have to imply destruction. It means "beginning."

This isn't a mythology heavy show, but if they wanted to they could just write off the confusion by saying different characters have different interpretations of what the Metalocalypse is.

Maybe they're starting the metalocalypse AND helping folks through it.

Crozier and Ravenwood were wrong. That was always pretty clear. I think Selatcia needs them for a sacrifice or something.