I don’t have any problems with store cards in general. I see them as a mutually beneficial agreement between retailers and frequent customers. It allows the retailer to capture a portion of the transaction revenue that would normally go to a third party (and some extra data about the customer), and in return pass on some of the savings to the customer in the form of discounts and rewards.
Sorry; that’s not a good product at all.
There are loopholes to this that make Prime much cheaper though.
For example, Prime Student [1] is $6.49/month or $59/year.
The EBT subsidized Prime membership mentioned elsewhere in the thread is $5.99/month (no annual discount).
You can also use Amazon Household [3] on an existing Prime membership to qualify multiple people in the household as Prime members. All members get the 5% benefit, not just the card holder. I doubt this stacks on the student version but it definitely does on vanilla Prime and likely on the subsidized version as well.
[1]: https://www.amazon.com/Amazon-Student/b?node=668781011
This assumes that one won't make use of their Prime benefits.
You factor in the cost of the Prime membership in the break-even calculation, but as someone else noted, that does not count the value of other Prime benefits. I was already a Prime member when the store card was introduced, which means I was valuing those benefits at ~$120/yr on their own.
Different people have different shopping needs/preferences. I have no trouble conceiving of the idea that what might be a good value to me might not be for someone else. In your case, I wonder how you are able to say "Sorry; that’s not a good product at all" with such conviction when there are so many people out there (~100 million) with Prime memberships in the US.