It appears that a WTO panel can be too deferential in applying its standard of review under the SPS Agreement. This is from Monday's Australia - Apples AB report:
356. In considering further the Panel's approach to analyzing whether New Zealand's proposed alternative measures meet Australia's appropriate level of protection, we note that the Panel repeatedly stated that it had to be careful not to "slip into conducting a de novo review". The Panel's caution was, however, misplaced. Caution not to conduct a de novo review is appropriate where a panel reviews a risk assessment conducted by the importing Member's authorities in the context of Article 5.1. However, the situation is different in the context of an Article 5.6 claim. The legal question under Article 5.6 is not whether the authorities of the importing Member have, in conducting the risk assessment, acted in accordance with the obligations of the SPS Agreement. Rather, the legal question is whether the importing Member could have adopted a less trade-restrictive measure. This requires the panel itself to objectively assess, inter alia, whether the alternative measure proposed by the complainant would achieve the importing Member's appropriate level of protection. The fact that, in the present case, the alternative measures proposed by New Zealand in the context of its claim under Article 5.6 had also been assessed in the IRA did not alter the nature of the Panel's task under Article 5.6.
What this says to me is two things: (1) in the Appellate Body's view, the standard of review is different under different provisions, and it is important to follow the text of the provision at issue in determining the standard to apply; and (2) the SPS Agreement standard of review may not be as deferential under certain provisions as some people might like.