I think there are two main points of disagreement I'm seeing here.

First, and more superficially, there is a disagreement about the statement "Given x, we should expect to see y." I argue that y is definable, but so far unobserved. You seem to be saying that y isn't even definable given the fundamental differences between species.

Here's why I don't think that's true. So long as we agree on what x is, where x is some form of communication (ie an intentional passing of information from one being to another, and yes I know the word "information" is doing a LOT of heavy lifting there, as are the words "intentional" and "passing" for that matter), then I think we should be able to draw inferences about the kind of behavior we would expect to see if that's happening.

And if it doesn't happen in the wild, we can set up experiments in the lab under controlled conditions, and see if it shows up there. My argument is that we only find y in the lab, and only when we manipulate the conditions in specific ways that don't exist in the wild.

The second, and deeper point of disagreement, concerns the meaning of x, and how it arises as a natural phenomenon. What if language actually requires certain cognitive prerequisites? In another article I argued that consciousness is logically and biologically dependent on theory of mind, and not the other way around. If we weren't social animals, we wouldn't need to think about our mental states. We would just have them, and then act accordingly. It only occurs to us to think about our own mental states if we're already spending a good deal of time thinking about those of others.

And when it comes to effective communication, you do have to think about how your signs are being interpreted, so maybe theory of mind is a prereq to language. Lots of animals have it, but they're mostly social mammals. You don't see evidence of theory of mind (which can be tested for in the lab) among most other animals.

You brought up the valid point that many animals don't have opposable thumbs, and so it's no surprise that they don't make complex tools and refashion their worlds. But that's interesting, isn't it? Humans aren't the only toolmakers, and evolutionary anthropologists have identified "tool" as a basic ontological category that we and other species seem to employ when dealing with objects.

But to see a tool you have to see metaphorically. You have to see that a rock isn't just a rock, but also a hammer. Maybe tool use is a prereq to language, because it trains the mind to think of things as having multiple layers of meaning, a phenomenon of which language is the example par excellence.