Let me try to explain this scenario using different words.
I definitely understand that you think “Genealogical Adam” (“Geneal.Adam”) is supposed to convince skeptical Creationists that they can trust science. But this is not actually how @Swamidass or I present his scenarios.
The scenarios are designed to to “provide relief” to those who are caught up in the dynamic tension between those who see too much Biblical investment in a historical Adam to ignore the idea of an historical Adam - - but, who also see that there is so much scientific evidence supporting an ancient Earth, or the common descent of humans from the primate branch of the animal kingdom, that they struggle with anxiety or indecision regarding the possibility that they are misinterpreting what they see in the Bible vs. what they see in the scientific record.
So, right away, @pevaquark, we don’t expect every Creationist to find the “Geneal.Adam” scenario as answering a need.
But the scenario does do two things:
 In years past, I would attempt to dissuade a Creationist from accepting the notion of Original Sin. I would try to persuade my audience that if millions of Eastern Orthodox Christians can thrive without any reference to Original Sin, they could too! The problem, of course, is that Western Creationists are very keen on Original Sin - - and they can’t imagine letting it go. [Frankly, it’s like Western Christianity is an entirely different religion!]
So now I don’t even have to struggle with a Creationist who adheres to Original Sin. It is no longer a point of contention between us (this is part of the “Peaceful” thing of PeacefulScience.Org). If they want Original Sin, they can have it!
 And the other thing that “Geneal.Adam” does is provide an intermediate point in the Creation/Evolution spectrum which is much closer to conventional Creationist views. Let’s suppose a Creationist has a choice between attending two different “coffee cake” sessions, sponsored by Christians in the science professions, on how to interpret the Bible regarding Creationism versus Evolution:
(a) one session will focus on how Adam and Eve can be seen as “figurative” or “allegorical figures”;
(b) and the other session starts with the idea that God used special creation to create just one man and one woman (in the midst of a pre-existing population of evolved humans)! In relative terms, this is such a tiny episode of God’s miraculous power there is really no way for science to definitively say it could never have happened.
This is quite analogous to the millions of modern Christians who don’t let Mary’s birth of Jesus (or His resurrection) interfere with their reliance on, and confidence in, Science. Adding one more amazing, but still tiny, miracle of God creating just 2 humans, is not nearly the same as the usual Creationist who throws the entire corpus of physics, chemistry and biology out the window… because he thinks he has to oppose any idea that animals evolved in order to justify Original Sin.
Peva, you know plenty of Creationists personally, right? Even hard-core Creationists, right? Do you think that even the most militant of Creationists would prefer to go to the gathering where the starting point is “Adam is really just an allegory!” Or do you think they would be rather intrigued by the opportunity to speak with Christians who already accept the idea that at least Adam and Eve were specially created?