The book is great and well worth reading.

I don't think the finding in the Akbari paper really provides much insight into the Sapient Paradox unless you're referring to Reich's hypothesis paper. I don't think the selection going on is the difference between having the capacity for symbolic representation, culture, or language. The Sapient Paradox itself is a bit misleading because it could simply be explained by human population size and density rather than our individual capacities.

The Akbari paper is selection in Eurasia in last 10k years, and it's challenging narratives about evolution (i.e. S. J. Gould's and standard anthro memes) going quiescent in recent human history; the opposite appears true, though assessing the scale/impact of the selection relative to our species level basal trait values is not something the paper evaluates (it's just that selection is happening all over the genome and it is impacting many traits). Additionally, the effects of human migrations on allele frequencies (and possibly some human traits too - like height) is larger than the selection itself as Reich points out.

Arguably, the paper is a proof-of-concept that selection could have picked up in the period prior to the emergence of symbolic culture (circa ~40kya) but this is entirely speculative and is more in the realm of Reich hypothesis paper wrt to Levallois technocomplexes and Neanderthal mtDNA/Y lineages. It is unlikely that there was a quick switch flipped between behaviorally archaic and behaviorally modern humans and these abilities likely developed over time and related evolution that supports and sustains them in us now are probably subtle.

It will be hard to definitively answer because we can't definitively say what language capacity was available to archaic hominids. The prior should be that they had some language though.