Ok, he's most likely wrong.

Interbreeding is pretty much proven.

Do you know why he thought they didn't have strong language skills and how he linked that to deception and such or was he guessing?

Because we have genetic tests nowadays, and it looks like they all bred in from the high percentages people have.

Interbreeding did happen but it’s probably not true that Neanderthals got wholesale assimilated into Homo sapiens. More that there was some low level of interbreeding.

I recommend reading the book, and also I would not recommend dismissing a respected book in one sentence, but I will say that the argument is largely anthropological. that the millions of years of human existence without development into more advanced civilizations can best be explained by language and oral history. More specifically, the ability to think in abstract and communicate it to others.

> Interbreeding did happen but it’s probably not true that Neanderthals got wholesale assimilated into Homo sapiens. More that there was some low level of interbreeding.

Why is it probably not true? It's the simplest reasoning. Why did they have to be deceived through language or annihilated, but slightly fornicated?

> I recommend reading the book, and also I would not recommend dismissing a respected book in one sentence

Seems reading the book wouldn't help me if you read it and can't argue the points on it's behalf.

I'll ask this again:

Do you know why he thought they didn't have strong language skills and how he linked that to annihilation via deception and such or was he guessing?

Wouldn't current percentages depend more on how adaptive those particular genes are than what the starting percentage was? How many generations between then and now?