The structure of the argument as presented in the book is “we see this sound symbolism in onomatopoeia” and gives a very large list of examples, followed by “t

The structure of the argument as presented in the book is “we see this sound symbolism in onomatopoeia” and gives a very large list of examples, followed by “this can be used to explain other phenomenons such as [insert parents statement]” You are right that it is interesting how and if ko-so-a-do fits this pattern, but I don’t think it’s a “gotcha” against sound symbolism in Japanese.