I wholeheartedly agree that people should be able to own their own housing, but I don't see the two as mutually incompatible in the larger scheme.
> The mental gymnastics are impressive. It’s not a good thing that Costco gets to expand to housing.
My definition of mixed-use development would include the case in TFA: Costco adding housing units above their store. Housing which you explicitly said is 'not a good thing'. I might agree with you, if Costco were slapping down a subdivision of company housing. But they're not, they're adding housing units above a proposed store in a mixed-use approach. This seems like a net good.
There could be a whole (cynical) side conversation as to whether or not Costco is adding these housing units simply to meet the criteria which allow for the expedited approval of this proposal, of course.