I have actually read some of the resources AND been there whilst customers received advice from lawyers. From what I had understood this model looked dubious.
I have not seen a discussion of this that didn't just end up in talking about morals. Even excluding this I really only wanted input from experts - answers from actual lawyers about GDPR have surprised me compared to what developers had assumed about it...
NB If I had a customer that proposed this model I would still insist that they consulted with their own legal advice before proceeding!
Given what you have said, perhaps the literature is not as obvious as I thought. As far as this model is concerned, it would not be compliant with the law as I read it and as I have had it explained to me. I don't deny that a party with enough money might be able to muscle a reading into existence that allows them to do this anyway, but that is I think an established risk of the legal system. For now we must operate with the law as written and broadly interpreted inside the EU.
Reading the guidelines is not the tricky part of GDPR. The hard part is: "I have a website, am I compliant or what do I have to change to become compliant?" Mapping the guidelines on to real world systems is where the difficult analysis comes in.
But I guess that the average lawyer knowledgable on GDPR issues would struggle to sort an array even in O(n^2) time so what do they know...
I.e. all things are simple to those that understand them!