If web scraping is legal then hitting the public api Amazon shouldn’t also be legal?

not necessarily according to the courts. there are a number of cases where scale has been the line between permissible and not - e.g. it's fine to scrape ebay, it's not fine to build an ebay scraping business.

courts haven't always ruled that way but there's definitely precedent!

https://en.wikipedia.org/wiki/EBay_v._Bidder%27s_Edge

Yes, but this case isn't about that -- it is about logged in accounts.