Google thrives on messy heuristics so it is perhaps unsurprising that they would view the problem from this perspective. I tend to agree with you that optimally

Google thrives on messy heuristics so it is perhaps unsurprising that they would view the problem from this perspective. I tend to agree with you that optimally all email should be read (and that this is realistically achievable in most cases), in which case the priority inbox feature is just a palliative and not a cure.