It may be the case the sorts of changes the result from the fall that Young Earth Creationists envision are overstated. So, "changed the universe" may have a lot more nuance in Keller's (and my) view than you suggest.
However, the Reformed and generally Christian position is that sin is an intrusion into a sinless world. "State of perfection" may also need some nuance...many Christian traditions hold to an idea of a subsequent consummation even had Adam and Eve not sinned, i.e. a move from a probationary period to an eternal glory where sin is not even possible, as we expect to be the case when we experience glorification in the New Heavens and New Earth.
But the idea that God created humanity with a sinful, fallen nature seems fundamentally at odds with the Biblical account. The doctrine of the Fall says that things aren't what they are supposed to be and even how they were created. There was innocence, not perfection.
You shouldn't get hung up on the idea that there's no evidence in the scientific/historical record of such a paradise. It may have been short-lived. Martin Luther suggested that Adam didn't make it past his first Sabbath. It also may have been restricted spatially to the Garden as well. You may protest that this means that we'll never find evidence for such a thing in the natural world. Fine. I don't base my belief in such a thing on evidence from the natural world, but from scripture.
Finally, and this comment applies to all my posts in this thread (and to others' posts as well). Neither the Bible nor science tell us this story in detail. The scenarios that I, Keller, Leo, Collins, Kidner, etc. propose are highly speculative attempts to make sense of both accounts. i wouldn't exactly call it "concordism", especially because that's a dirty word around here, but it is an attempt to make sense of two seemingly disparate revelations, confessing that both are authored by the same Person.
I am quite comfortable with the idea of docta ignorantia. We may never know how it all fits together, but we can affirm both the evolutionary claims and the Reformed theology claims knowing that God knows how they fit together. Both claims are rooted in a proper Christian epistemology, albeit two very different methods of attaining knowledge.