I think you intended Berwick & Chomsky (2016) as the citation. Since it's not in the references, here is the citation:

Berwick, R.C. & Chomsky, N. A. (2016). Why only us? Language and Evolution. Cambridge, MA, MIT Press.

Though there is also:

Bolhuis, J. J., Tattersall, I., Chomsky, N., & Berwick, R. C. (2014). How could language have evolved? PLoS Biology, 12(8), e1001934.

While it's true that Merge would not have been very useful for interpersonal communication without words it isn't clear to me that it's logically impossible or that "Merge sans words" would not have been useful for internal thought processes.

This point ("Merge prior to externalization") is discussed in their book, and you have provided a longer comment on that in your review (Studdert-Kennedy, M., & Terrace, H. (2017). In the beginning: A review of Robert C. Berwick and Noam Chomsky’s Why Only Us. Journal of Language Evolution, 2(2), 114–125.). So perhaps you will review your arguments in more detail on this blog later.