I think you are missing the point and are perhaps letting this app vendor create an impression of a large problem based on anecdotal evidence. Perhaps they are just whining because they don't want to lose all that data. I have no idea that that is the case, but we can't rule it out.

Tons of people falling into these alleged traps? Really? What is that based on?

Apple is saying they want their platform to support personal privacy. If an app on their platform offers third party sign-ons that are known to abuse personal privacy, that app must offer Apple's solution that respects personal privacy. Despite it being an imperfect solution, I personally am thrilled that I have that option and I'm happy with Apple taking a stand on one of the most important issues today and going forward.

Some occasional customer support issues vs. providing customers with a real solution to significant privacy issues. From a user perspective the value of having such a choice is high.

Nobody is blaming users. Frankly, I think users are smarter than we typically assume. The support situation is really pretty trivial. If you save the onboarding email sent to the anonymized email address, you've got all you need to interact with an app customer support. People will quickly learn this and get on board if they want the privacy benefit. Its just not a big deal.

Apple's role is about increasing privacy and respecting their user's right to privacy. I fully acknowledge that. Does this create some hassle for app vendors? Yes, but I don't care about that in relation to the greater gain.