If there was some non-negligible probability that the study was bad, RationalWiki would, given their dislike for chiropractics, have seized upon that and discussed it explicitly, would they not?
They describe the Cochrane study as "weak evidence" that chiropractic is as effective as other therapy. This implicitly includes some non-negligible probability that the benefit is less than the study seems to say it is.
I just finished the first draft of my essay, "Are Sunk Costs Fallacies?"; there is still material I need to go through, but the bulk of the material is now there. The formatting is too gnarly to post here, so I ask everyone's forgiveness in clicking through.
To summarize:
(If any of that seems unlikely or absurd to you, click through. I've worked very hard to provide multiple citations where possible, and fulltext for practically everything.)
I started this a while ago; but Luke/SIAI paid for much of the work, and that motivation plus academic library access made this essay more comprehensive than it would have been and finished months in advance.