There are many other metrics that do not involve AB testing. You can just survey customer experience before, during and after a purchase for example. I never said to throw out all metrics.

With AB testing your are optimising for a specific outcome. Usually higher conversion. As pointed out in the article eventually you'll end up with a bunch of colourful buttons and scary texts that persuade the user to click. A lot of the "only 2 seats/rooms available" are lies to scare the user into a conversion.