This strikes me as a perfect description of the core problem. Whenever I think about this, what sticks out to me is that other animals do all sorts of things that look like "intelligence," or at least cognition, and they do it totally without language. My cat clearly recognizes objects, assigns them different values ("scary," "tasty," "fun to play with"), interacts with them in some kind of loop, even predicts their behavior to some extent and acts curious about them (it was really fun to watch her try to figure out the construction guys when I had some work done on my house over a period of a few days). These strike me as much more foundational aspects of intelligence than language. Language has of course immeasurably contributed to what makes human cognition and intelligence, but it's almost certainly built on these pre-linguistic foundations. Another very good hint in this direction is all of the non-verbal thinking that humans have done. Einstein has a famous quote about thinking visually and physically, without using language at all. All of these are powerful suggestions that something else is going on, and most likely some aspect of these things are necessary for true intelligence.