The real tragedy is that they didn't need to do it. They could have released stat blocks for the Dark Lords just fine, because Ravenloft is possibly the most GM-centric setting in D&D. In Ravenloft, player characters don't get to combo off unless the GM explicitly allows it. They don't get to fight the Dark Lord in their own terms unless the GM lets them. It's not fair, and it's not meant to be. It's a setting where the world is actively against the party, and it's also a setting where the narrative dictates where things go a lot of the time.
You could legitimately make a Dark Lord with 1HP. But the catch is that said Dark Lord cannot be found/fought/injured until the party retrieves a specific item, performs the right ritual, solves a difficult puzzle, and/or convinces the right person to help them. The Dark Lord only dies when the GM says so.