I'm kind of bored defending Dingwall when I'd personally have him as 3rd choice behind Atkinson and Ojomoh (possibly slipping back further if Ma'asi-White or Woodward kick on).
However, I think he's been either fine or good in most of his appearances. He was poor at the weekend, but if he hadn't thrown the intercept vs. Australia, I don't think anyone would have picked that game out as a notably poor performance.
Describing the situation with the midfield as 'a mess' is harsh IMO. I think Atkinson would have started had he been fit, but Dingwall's performances in the 6N rightly had him in the box seat to come back into the side ahead of Ojomoh who has been in form but is untested at this level. The alternative is either a third untried combination (Lawrence + Freeman or Slade + Freeman) or return to the Lawrence/Slade combo that has never really worked.
Personally, I think the mistake was accommodating Freeman's desire to play 13. I do think it's a worthwhile experiment but given Lawrence's form, I would have resisted the temptation to do it and played Dingwall and Lawrence for both games to build familiarity.
Now I think it's a case of backing Dingwall for the rest of the Autumn and hoping he steps-up or bring in back Slade. I see a bigger upside in the former, but vs. NZ I can understand why Slade's experience might be preferred.