Yes and no. If editorial came in and forced changes into the story, that's not on Williamson. But that's also pretty normal in this industry and writers are expected to roll with such changes and make them work. Williamson didn't pull that off.
It's probably not his fault. We've probably all had jobs where everything is going smoothly until management comes in with a mouth full of stupid ideas and things go off the rails, and nothing we do can fix it. This was pretty much DC during the New52, when it was common practice to change plans at the last minute, sometimes even after the art had been finalized.
So I have a hard time putting a lot of blame on Williamson for all that, but end of the day he took a gig doing a big Event, which are always real heavy on editorial mandates, and he didn't manage to juggle whatever changes DC threw at him. And he's been with the company long enough to know how they do things, so we can't say he got caught off guard by DC's heavy handedness.
What I *do* blame Williamson for is the basic story, questionable pacing, and sometimes-awkward dialogue. Whatever changes editorial made, the basic premise of the story was still weak and repetitive, just a blender full of previous Crisis, "everyone is dead!" stories we've already read. I appreciate that Williamson put Nightwing front and center, and the story wasn't all bad, but in the end Dark Crisis didn't live up to the legacy it was trying to emulate.
But he did right by Nightwing, and that earns a *lot* of forgiveness in my book. Plus, Williamson is usually a quality talent so I'm not hating on the guy here. This story didn't work out, but whatever, I'm still looking forward to his Arrow.