Added Nesquik to the table.
if you make that kind of analysis with anything at Costco you are always going to buy the thing at Costco, which is the fundamental trade off of Costco, giving up variety for good prices on large quantities.
This kind of analysis just tells you what the costs are. If price is all you care about, then sure, you'll just get everything at Costco. But usually, there's much more at play than just price. This would tell you how much you're paying for the other things you might care about, thus enabling you to make a decision on whether or not it's worth it.
It allows you to compare between different package sizes for the same product, but not between different products. Our goal here is to compare different products.