The exact same thing happened with Demon's Souls, though. The project was a massive failure, and Miyazaki just asked "can I try to fix it?", so he basically remade the whole thing to his tastes, mostly because From didn't care about it anymore, and from what was initially going to be sent to die, began Miyazaki's carreer as one of the best game designers in the industry.
Development hell also doesn't apply to the DLCs, and Eleum Loyce wasn't nearly as good as Shulva or Brume Tower, in my opinion.
Also, this would mean every game not made in development hell is as good as Dark Souls, which isn't true at all.
Miyazaki has a very hands on approach to the game design, he oversees every aspect of it, including level design, and I remember reading that he writes every item description and chooses every single name himself.
I'm not a fan of the hyperboles thrown at Dark Souls II either, but trying to make Miyazaki's presence less relevant than it is is just as crazy.
He's responsible for at least two of the three most important aspects in the series, to me, which are Level Design, Boss Battles and the Lore.