It certainly diminishes the usefulness of the rule of thumb if you add “and you’re still the product anyway even if you’re paying” to the end of it.

Sometimes you are neither the customer nor the product. (e.g. a service like wikpedia or a project like linux)

I think the context in which the phrase "if you're not the customer, you're the product" is often used implies that we should upgrade our relationship by paying, however this is not necessarily the case as shown here.

The comparison worked for Facebook at the time, because having a directly reachable and targetable audience was groundbreaking at the time (2006-2012) In 2022, audiences are everywhere and getting them stratified and connected is not hard. Therefore, many companies are exploiting this to cross- and up-sell their products. I guess my point is that product != audience.