Or, to be brutally honest, the audience. Super-intelligent characters might well be able to discuss very complex ideas with minimal actual talking, and with a lot of unsaid implications about certain aspects. Such interactions could be rather difficult to follow and/or appreciate for us poor regular human types. Thus there's a degree of suspension of belief, or an assumption that there is an aspect of translation convention going on. You could even argue that as we see most of the action from the SI's viewpoint, we're also seeing ring-generated translations of things the characters may not be specifically saying out loud.
Actually, communicating with minimal actual verbiage and lots of innuendo, implication, and expression-reading is more a function of empathy and intuition (or, in D&D terms, "Wisdom") than raw intelligence (which would include logical reasoning and ability to analyze presented data, as well as to detect patterns and follow them to their conclusions).
Not to be overly egotistical, but I am generally considered unusually intelligent, and I can attest that this doesn't help me nor my similarly intelligent friends to have a lot of "unspoken" high-information-density conversation. Shared culture aids in that, as we can make references and use commonly-held verbal and gesticular shorthand, but when speaking on nearly any subject, we tend to wax sesquipedalian in our loquatiousness, seeking great precision in clearly expressing the nuances of our ideas to each other. Only when we're very much on the same wavelength do we show the tendency of paired geniuses in fiction to use incomplete sentences the other can fill in, and that doesn't last long before we find something where our thoughts diverge on a matter and we must stop and clarify in great detail.
Dox and Hinon are having a negotiation; they are not on the same wavelength and thinking along the same lines. Efforts of persuasion are necessarily going to require a great deal of precise communication to get across the logical reasons for and against proposed courses of action.
Additionally, the legendary ability of the hyperintelligent to "talk over the heads" of less-brilliant people is usually more a function of education than genius, though ease of understanding complex concepts helps. It doesn't involve leaving thoughts incomplete or having much of the exchange unspoken; it involves speaking essentially a different language (or at least a heavily-accented dialect). Usually in much longer and more complex sentences to cover much more complicated and hard to express subjects.