How is it petty to point out a flaw in a product you paid for? I get the subscription doesn’t grant you access anytime, but when a product is paid for the customer feels some entitlement to criticize it if it’s not working as intended. That’s not petty, that keeps companies from constantly doing a bad job.
Based on your theory Yelp, Metactitic and other review sites are “petty”. No, they are simply an outlet for the customer to let people know how the company is doing. In this case they GROSSLY underestimated the number of servers needed and the servers they allowed people to sign up on to reserve names had zero chances to work well.